               XTide:  Harmonic tide clock and tide predictor

                            San Francisco graph

Preface

   Welcome  to the verbose documentation for XTide 2.  If you are reading
   this  as a text file, please be aware that the text was extracted from
   the  illustrated  HTML  version  of  the documentation that resides at
   [1]http://www.flaterco.com/xtide/.   The  web version may also be more
   up-to-date than what you are reading.
     _________________________________________________________________

    THE XTIDE SOFTWARE DISTRIBUTION IS AVAILABLE FROM:
    [2]http://www.flaterco.com/xtide/files.html
     _________________________________________________________________

   [3]Buoy in the mist

Contents

     * [4]License and disclaimer ("NOT FOR NAVIGATION," "ABSOLUTELY NO
       WARRANTY")
     * Verbose documentation
          + [5]Introduction
          + [6]System requirements
          + [7]Installation instructions for Unix, Cygwin, or Mac OS X
          + [8]Available ports for non-Unix platforms
          + [9]Modes and formats
          + [10]Using the interactive interface
          + [11]Advanced usage
          + [12]Using the command line interface
          + [13]Running the web server
          + [14]Customizing XTide
          + [15]What to do if your location isn't listed
          + [16]Quirks, limitations, and bugs
          + [17]FAQ
          + [18]Design notes
          + [19]Credits
          + [20]Bibliography
          + [21]Appendix A -- Historical predictions and Y2038 compliance
          + [22]Appendix B -- Application of offsets for Min Flood and
            Min Ebb events
          + [23]Appendix C -- Making calendars fit onto a single page
     * Short attention span documentation for experienced XTide users
          + [24]Differences from XTide 1
          + [25]Quick install instructions
          + [26]Change log
          + [27]News (current XTide developments)

   The XTide software distribution resides at
   [28]http://www.flaterco.com/xtide/files.html.

   Hint:   If  you  have  no idea what all this is about, try reading the
   [29]FAQ first.

   -- David Flater (dave@flaterco.com)

References

   1. http://www.flaterco.com/xtide/
   2. http://www.flaterco.com/xtide/files.html
   3. http://www.flaterco.com/
   4. http://www.flaterco.com/xtide/disclaimer.html
   5. http://www.flaterco.com/xtide/introduction.html
   6. http://www.flaterco.com/xtide/sysreq.html
   7. http://www.flaterco.com/xtide/installation.html
   8. http://www.flaterco.com/xtide/ports.html
   9. http://www.flaterco.com/xtide/modes.html
  10. http://www.flaterco.com/xtide/interactive.html
  11. http://www.flaterco.com/xtide/advanced.html
  12. http://www.flaterco.com/xtide/tty.html
  13. http://www.flaterco.com/xtide/xttpd.html
  14. http://www.flaterco.com/xtide/settings.html
  15. http://www.flaterco.com/xtide/harmonics.html
  16. http://www.flaterco.com/xtide/bugs.html
  17. http://www.flaterco.com/xtide/faq.html
  18. http://www.flaterco.com/xtide/design.html
  19. http://www.flaterco.com/xtide/credits.html
  20. http://www.flaterco.com/xtide/bibliography.html
  21. http://www.flaterco.com/xtide/time_t.html
  22. http://www.flaterco.com/xtide/mincurrents.html
  23. http://www.flaterco.com/xtide/pound_to_fit.html
  24. http://www.flaterco.com/xtide/xtide1diff.html
  25. http://www.flaterco.com/xtide/quickinst.html
  26. http://www.flaterco.com/xtide/changelog.html
  27. http://www.flaterco.com/xtide/news.html
  28. http://www.flaterco.com/xtide/files.html
  29. http://www.flaterco.com/xtide/faq.html

################################################################

   [1]-> Next [2]Contents

Icon License and disclaimer

   NOTE.  The license and disclaimer appearing below applies to the XTide
   program  itself.   For  information  about permissions on the harmonic
   constants, see
   [3]http://www.flaterco.com/xtide/harmonics_boilerplate.txt         and
   [4]http://harmonics.unh.edu/xtide/harmonics_boilerplate.txt.

                    XTide Copyright © 1998 David Flater

   This  software  is  provided under the terms of the GNU General Public
   License,  either  version  2  of  the License, or (at your option) any
   later version.

   Although  the  package as a whole is GPL, some individual source files
   are public domain.  Consult their header comments for details.

                             NOT FOR NAVIGATION

   This  program  is  distributed in the hope that it will be useful, but
   WITHOUT   ANY   WARRANTY;   without   even  the  implied  warranty  of
   MERCHANTABILITY  or  FITNESS  FOR  A  PARTICULAR  PURPOSE.  The author
   assumes  no  liability for damages arising from use of this program OR
   of  any  'harmonics  data'  that  might  be  distributed with it.  For
   details, see the appended GNU General Public License.

   (Accurate  tide  predictions  can only be made if the 'harmonics data'
   for  the  relevant location are good.  Unfortunately, the only way the
   maintainer  of  those  data  has  of knowing when they are bad is when
   someone  with access to authoritative tide predictions or observations
   reports  a problem.  You should not use this program or any data files
   that  might be distributed with it if anyone or anything could come to
   harm  as  a  result of an incorrect tide prediction.  NOAA and similar
   agencies  in  other  countries  can  provide  you  with certified tide
   predictions if that is what you need.)

   XTide's predictions do not incorporate the effects of tropical storms,
   El  Niño, seismic events, subsidence, uplift, or changes in global sea
   level.
     _________________________________________________________________

   The  tide prediction algorithm used in this program was developed with
   United  States  Government  funding,  so  no proprietary rights can be
   attached  to  it.   For  more  information,  refer  to  the  following
   publications:

     Manual  of  Harmonic  Analysis  and  Prediction  of Tides.  Special
     Publication  No.  98,  Revised  (1940) Edition (reprinted 1958 with
     corrections;  reprinted  again  1994).   United  States  Government
     Printing Office, 1994.

     Computer  Applications  to  Tides  in  the  National  Ocean Survey.
     Supplement  to  Manual of Harmonic Analysis and Prediction of Tides
     (Special  Publication  No.  98).   National Ocean Service, National
     Oceanic   and   Atmospheric   Administration,  U.S.  Department  of
     Commerce, January 1982.
     _________________________________________________________________

                    GNU GENERAL PUBLIC LICENSE
                       Version 2, June 1991

 Copyright (C) 1989, 1991 Free Software Foundation, Inc.
     51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 Everyone is permitted to copy and distribute verbatim copies
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     _________________________________________________________________

   [5]-> Next [6]Contents

References

   1. http://www.flaterco.com/xtide/introduction.html
   2. http://www.flaterco.com/xtide/xtide.html#contents
   3. http://www.flaterco.com/xtide/harmonics_boilerplate.txt
   4. http://harmonics.unh.edu/xtide/harmonics_boilerplate.txt
   5. http://www.flaterco.com/xtide/introduction.html
   6. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

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   [4]Bald Head Cliff, Ogunquit, Maine, 1998-06-15

Introduction

   XTide  is  a  package  that provides tide and current predictions in a
   wide  variety of formats.  Graphs, text listings, and calendars can be
   generated, or a tide clock can be provided on your desktop.

   XTide can work with X-windows, plain text terminals, or the web.  This
   is   accomplished  with  three  separate  programs:   the  interactive
   interface  (xtide),  the  non-interactive  or  command  line interface
   (tide), and the web interface (xttpd).

   The  algorithm that XTide uses to predict tides is the one used by the
   [5]National  Ocean  Service  in  the  U.S.   It  is significantly more
   accurate  than  the  simple  tide clocks that can be bought in novelty
   stores.   However, it takes more to predict tides accurately than just
   a spiffy algorithm--you also need some special data for each and every
   location  for which you want to predict tides.  XTide reads these data
   from harmonics files.  See [6]http://www.flaterco.com/xtide/files.html
   for details on where to get one.

   Ultimately,  XTide's  predictions can only be as good as the available
   harmonics   data.    Due   to  issues  of  data  availability  and  of
   compatibility  with  non-U.S.  tide  systems, the predictions for U.S.
   locations  tend to be a lot better on average than those for locations
   outside  of  the  U.S.  It is up to you to verify that the predictions
   for   your  locale  match  up  acceptably  well  with  the  officially
   sanctioned ones.
     * Deviations  of  1 minute from official predictions are typical for
       U.S. locations having the latest data.
     * Deviations  of  20  minutes  are typical for non-U.S. locations or
       U.S. locations that are using obsolete data.
     * Much longer deviations indicate a problem.

   The XTide software distribution resides at
   [7]http://www.flaterco.com/xtide/files.html.

   XTide   and   its   documentation   are  maintained  by  David  Flater
   (dave@flaterco.com).
     _________________________________________________________________

   [8]<- Previous [9]-> Next [10]Contents

References

   1. http://www.flaterco.com/xtide/disclaimer.html
   2. http://www.flaterco.com/xtide/sysreq.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://oceanservice.noaa.gov/
   6. http://www.flaterco.com/xtide/files.html
   7. http://www.flaterco.com/xtide/files.html
   8. http://www.flaterco.com/xtide/disclaimer.html
   9. http://www.flaterco.com/xtide/sysreq.html
  10. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

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   [4]Cutler in the fog

System requirements

  Hardware

   The  base  configuration  for  which XTide 2 was written was a 166 MHz
   Pentium  PC  with  32  MiB of RAM (circa 1997).  XTide version 2.9 was
   successfully  tested on the same PC in 2007, although by that time the
   RAM  had  been  expanded to 96 MiB.  Comparable non-PC hardware (e.g.,
   Sun Sparcstation) also works.

   XTide  uses  less  than  10  MB  of  memory  for a typical interactive
   session.

  Operating system

   XTide  is  Unix software.  It is intended to compile and run correctly
   on  any  reasonably modern version of Unix.  However, I no longer have
   direct  access  to  any flavor of Unix other than Linux, so I can only
   make portability fixes if and when issues are reported.

   In  order  for  tide  predictions to have the correct Daylight Savings
   Time   (Summer   Time)  adjustments,  your  platform  must  provide  a
   sufficiently up-to-date version of the tz database.  This has recently
   become an issue again since the U.S. changed its Daylight Savings Time
   rules  for  2007.   If your time zone database is obsolete, you may be
   able    to    upgrade    it    using    the    latest   version   from
   [5]ftp://elsie.nci.nih.gov/pub/  or  by installing an operating system
   patch.

   XTide  has  been  ported  to a variety of other operating systems with
   differing  levels  of  success.   These  ports  will be discussed in a
   [6]later section.

  Software

   XTide  is intended to compile under any reasonably modern C++ compiler
   that  supports  the  Standard  Template Library.  However, I no longer
   have  direct access to any compiler other than GCC, so I can only make
   portability fixes if and when issues are reported.

   For GCC, "reasonably modern" means version 3.4 or newer.

   You  need  [7]bzip2  to  uncompress the files.  A list of libraries on
   which XTide is dependent is provided in the [8]next section.
     _________________________________________________________________

   [9]<- Previous [10]-> Next [11]Contents

References

   1. http://www.flaterco.com/xtide/introduction.html
   2. http://www.flaterco.com/xtide/installation.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. ftp://elsie.nci.nih.gov/pub/
   6. http://www.flaterco.com/xtide/ports.html
   7. http://www.bzip.org/
   8. http://www.flaterco.com/xtide/installation.html
   9. http://www.flaterco.com/xtide/introduction.html
  10. http://www.flaterco.com/xtide/installation.html
  11. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Prospect Harbor Pt. Light, Prospect Harbor, Maine, 1998-06-14

Installation instructions for Unix, Cygwin, or Mac OS X

  Assumptions

   These  installation  instructions  assume  that  you are building from
   sources   obtained  from  [5]http://www.flaterco.com/xtide/files.html.
   However, some Linux users may be able to shortcut this process:  XTide
   has been included in [6]Fedora and [7]Debian.  (Thanks to the relevant
   package maintainers.)

   These  instructions  also  assume  that you are building XTide version
   2.9.   Previous  versions  of  XTide  were  not  packaged  with [8]GNU
   automake,  so  the  installation  process was not as standardized.  In
   addition,  they  statically  linked with an included version of libtcd
   instead  of  using a shared libtcd that was installed separately.  For
   these  reasons  and  others  it is advisable that you upgrade to XTide
   2.9.

  Dependencies

   In  addition  to  the  minimal  set  of X11 libraries that pretty much
   everyone has, you need the following libraries:

     * [9]libXpm 3.4 or newer compatible version
     * [10]libpng version 0.96 or newer compatible version
     * [11]zlib (a.k.a. libz) version 1.0.4 or newer compatible version
     * [12]libtcd version 2.2 or newer compatible version

   XTide  2.9 will link with [13]libdstr (version 20070215 or compatible)
   if  it  is  found  on  the  system,  but  installing  it is completely
   optional.   If  it  is  not present, XTide will link statically with a
   bundled copy of Dstr.

   tide  and  xttpd  can  be compiled in the absence of X11 libraries and
   libXpm.  However, you still need the other stuff.

  Downloading

   Mandatory:   You need the XTide source code distribution, available in
   bzipped tar format at
   [14]http://www.flaterco.com/xtide/files.html#xtide.

   Mandatory:   You  need  at  least one harmonics file.  Harmonics files
   contain  the  data  that  are  required for XTide to predict tides for
   different  locations.   A  canonical harmonics file and information on
   getting others is provided at
   [15]http://www.flaterco.com/xtide/files.html#harmonicsfiles.

   Optional:   If you want to enable XTide to draw coastlines on the map,
   you will also have to download the World Vector Shoreline (WVS) files,
   which are available in bzipped tar format at
   [16]http://www.flaterco.com/xtide/files.html#WVS.

   WVS  is  optional  because  the  minimum recommended hardware (166 MHz
   Pentium  PC)  takes  16 seconds to draw shorelines for a hemisphere of
   the globe.  A 3.2 GHz P4 takes less than 1 second.

  Installing the harmonics file

   First you need to decompress it:

bzip2 -d harmonics-dwf-YYYYMMDD.tcd.bz2

   Then  move  it  to a permanent location, e.g., /usr/local/share/xtide,
   and make it world readable:

mkdir /usr/local/share/xtide
chmod 755 /usr/local/share/xtide
chmod 644 harmonics-dwf-YYYYMMDD.tcd
mv harmonics-dwf-YYYYMMDD.tcd /usr/local/share/xtide

  Installing the World Vector Shoreline files (optional)

    1. Create a directory to contain the WVS files.
    2. Change your current working directory to that directory.
    3. Unpack the tar file in that directory.

   Under Linux and any other system with GNU tar:

tar xvjf wvs.tar.bz2

   Elsewhere:

bzip2 -dc wvs.tar.bz2 | tar xvf -

  Unpacking the sources

   Under Linux and any other system with GNU tar:

tar xvjf xtide-2.xyz.tar.bz2

   Elsewhere:

bzip2 -dc xtide-2.xyz.tar.bz2 | tar xvf -

  Configuring

    I.  Specify the location of the harmonics file(s)

   There are two ways to do this.

    1. The first way is by setting the environment variable HFILE_PATH.

export HFILE_PATH=/usr/local/share/xtide/harmonics.tcd

       In  the  event that you have more than one harmonics file that you
       wish to use simultaneously, list them separated by colons.

export HFILE_PATH=/usr/local/share/xtide/harmonics-US.tcd:/usr/local/share/xtid
e/harmonics-EU.tcd

       Alternately,  make  sure  that they are by themselves in a special
       directory  and  specify that directory as the value of HFILE_PATH.
       If  an element of HFILE_PATH is a directory, XTide will attempt to
       load  every  file  in that directory (so be sure that they are all
       harmonics files!)
       If you are installing as root, then it is recommended that you add
       this  definition  to  a system-wide script such as /etc/profile if
       you have one.
    2. The  other  way  is  by  creating  the  file /etc/xtide.conf.  The
       environment  variable,  if  set,  takes precedence over the config
       file.
       If  a configuration file is used, the first line should consist of
       the value that would be assigned to HFILE_PATH:
/usr/local/share/xtide/harmonics-US.tcd:/usr/local/share/xtide/harmonics-EU.tcd

    II.  Specify the location of the World Vector Shoreline files (optional)

   Either  set  the  environment  variable  WVS_DIR  to  the name of that
   directory  or  supply  the  directory  name  as the second line of the
   configuration file /etc/xtide.conf.

    III.  Run the configure script

bash-3.1$ ./configure

   XTide  2.9 is packaged with the popular and portable [17]GNU automake,
   so  all  usual  GNU tricks should work.  Help on configuration options
   can be found in the CONFIGURE file or obtained by entering ./configure
   --help.

   The  web  server  xttpd is not necessary to use tide or xtide, so most
   users  needn't  worry about it.  However, if you plan to run it, there
   is additional configuration at this point.

   To  change  the  user and/or group under which xttpd tries to run (the
   defaults      are      nobody/nobody),     provide     the     options
   --with-xttpd-user=user  and/or  --with-xttpd-group=group to configure.
   If you want to run xttpd but you don't have root, you will have to set
   these  to  your  own  username and the name of some group to which you
   belong.

bash-3.1$ ./configure --with-xttpd-user=xttpd --with-xttpd-group==scarydæmons

   You can also set the webmaster address for xttpd this way.

bash-3.1$ ./configure --with-webmaster="somebody@somewehere.else"

    IV.  Other optional and alternative configurables

   --enable-time-workaround Work around Y2038 problem; disable time
   zones.  See [18]Appendix A -- Historical predictions and Y2038
   compliance.
   --enable-gnu-attributes  Use  with  g++ -Wall -Wextra to make warnings
   smarter.

   You  can  change  the  compile-time  defaults  (colors,  etc.)  set in
   config.hh  if  you  so choose.  However, the easiest way to set all of
   those  things  is  with the [19]control panel in the interactive XTide
   program.

   The  e-mail  address  for  feedback  in  xttpd  can also be changed by
   setting  the  environment  variable  XTTPD_FEEDBACK,  in  lieu  of the
   configure option mentioned above.

  Compiling

bash-3.1$ make
bash-3.1$ su
bash-3.1# make install

Special cases

  Don't have X11

   If  you  don't  have  any  version  of  X11 installed and just want to
   compile  xttpd or tide, generate a Makefile using ./configure and then
   type  'make  xttpd' or 'make tide'.  You will probably need to install
   the binaries by hand.

  CPU-bound platform

   If running on the minimum recommended hardware (166 MHz Pentium PC) it
   is  advisable  to  forego  installing  the  [20]World Vector Shoreline
   database.   If  a  true color display is present, graph drawing can be
   sped  up  enormously  by  turning off anti-aliasing (see [21]settings,
   XTide*antialias).

  Cygwin

  XTide can be compiled and run using [22]Cygwin, which is an emulated Unix
  environment for Windows that is free for typical non-commercial users.  The
  Cygwin distribution and its full license terms are available from
  [23]http://www.cygwin.com/.

  Cygwin packages are all versioned separately, so there is no baseline "Cygwin
  version" against which to test XTide.  Testing was most recently performed
  with XTide 2.9.2 using the collection of packages that was current as of
  2007-03-31.

  As of then, the quirks apparent after brief testing were as follows.

    1. If only building certain of the programs, you must type (e.g.)
       'make tide.exe' instead of 'make tide'.  'make tide' causes the
       automake-generated makefile to do something silly.
    2. Graph drawing in the interactive interface is an order of
       magnitude slower.  The slowdown can be mitigated by turning off
       anti-aliasing (see [24]settings, XTide*antialias).
    3. When you drag a window around, fine-grained exposure events for
       any overlapped windows are queued but not delivered until you drop
       it.  The resulting redraw behavior is suboptimal.
    4. When you resize a graph window, instead of delivering one
       ConfigureNotify event, Cygwin delivers a huge pile forming a
       continuum between the old size and the new one.^[25]1  This is
       worse than suboptimal as it can take a long time to resize the
       graph that many times.  Once again, the slowdown can be mitigated
       by turning off anti-aliasing (see [26]settings, XTide*antialias).

   Cygwin  used  to  have  worse  problems  than  that,  so  it is highly
   advisable to update your installation before compiling XTide.

  Mac OS X

  XTide should compile cleanly and run under Mac OS 10.3.3 or later.

  If the PNG package is installed via Fink ([27]http://fink.sourceforge.net/),
  use CPPFLAGS="-I/sw/include" and LDFLAGS="-L/sw/lib" to find the
  Fink-installed PNG files.

  A [28]native port to OS X is also available.
  IRIX

  Some SGI machines come with a broken make program.  Use GNU make.
  HP-UX

  Long ago, a user submitted the following flags to get XTide to compile using
  the aCC compiler under HP-UX.  If somebody still uses this platform and the
  flags are still needed, they can be supplied to configure:

bash-3.1$ CXX="aCC" CXXFLAGS="-Wc,-koenig_lookup,on +DAportable" LDFLAGS="-lPW"
 ./configure

   It  is  possible  that the latest configuration scripts add all needed
   flags automatically, but they have not been tested under HP-UX.

Troubleshooting

Q: XTide compiles, but when I try to run it I get an error like

error while loading shared libraries: libtcd.so.0: cannot open shared object fi
le: No such file or directory

   A:  Somehow,  g++  found  the  shared  library but your dynamic linker
   didn't.   To  get the dynamic linker to find the library, you can just
   add  its  directory  to the environment variable LD_LIBRARY_PATH.  For
   example, if you find the library in /usr/local/lib, you would add this
   to your .bashrc (if using bash):
export LD_LIBRARY_PATH=/usr/local/lib

   Or you would add this to your .cshrc (if using csh or tcsh):
setenv LD_LIBRARY_PATH /usr/local/lib

   Q:  XTide  2.8.3 or earlier compiles, but when run the following error
   occurs:
X Error of failed request:  BadName (named color or font does not exist)
  Major opcode of failed request:  45 (X_OpenFont)

   A: You need to install the Schumacher fonts.  These fonts were present
   on  every  X11  installation  until 2006, when Gentoo Linux made their
   installation  optional.   For  what it's worth, XTide 2.9 gives a more
   helpful error message that tells you which font it could not load.

   Q:  When  compiling  XTide,  I get an error involving xml-something or
   lex.xml.c.

   A:  For  XTide 2.9 or later, do make xmlclean and then try again.  For
   XTide 2.8.3 or earlier, run the script do_xml.sh and then try again.
     _________________________________________________________________

   [29]<- Previous [30]-> Next [31]Contents

   ^1 The Xlib Programming Manual says the ConfigureNotify event is to be
   generated when the resize request "actually completes."  Unlike Expose
   events, there is no mechanism for handling consecutive ConfigureNotify
   events  as  a  batch.  This suggests that the Cygwin interpretation is
   not what was intended.

References

   1. http://www.flaterco.com/xtide/sysreq.html
   2. http://www.flaterco.com/xtide/ports.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/files.html
   6. http://fedora.redhat.com/
   7. http://www.debian.org/
   8. http://www.gnu.org/software/automake/automake.html
   9. ftp://ftp.x.org/contrib/libraries/
  10. http://www.libpng.org/pub/png/libpng.html
  11. http://www.zlib.net/
  12. http://www.flaterco.com/xtide/files.html#libtcd
  13. http://www.flaterco.com/util/index.html
  14. http://www.flaterco.com/xtide/files.html#xtide
  15. http://www.flaterco.com/xtide/files.html#harmonicsfiles
  16. http://www.flaterco.com/xtide/files.html#WVS
  17. http://www.gnu.org/software/automake/automake.html
  18. http://www.flaterco.com/xtide/time_t.html
  19. http://www.flaterco.com/xtide/advanced.html#cp
  20. http://www.flaterco.com/xtide/installation.html#WVS
  21. http://www.flaterco.com/xtide/settings.html#antialias
  22. http://www.cygwin.com/
  23. http://www.cygwin.com/
  24. http://www.flaterco.com/xtide/settings.html#antialias
  25. http://www.flaterco.com/xtide/installation.html#fn1
  26. http://www.flaterco.com/xtide/settings.html#antialias
  27. http://fink.sourceforge.net/
  28. http://www.flaterco.com/xtide/ports.html#Mac
  29. http://www.flaterco.com/xtide/sysreq.html
  30. http://www.flaterco.com/xtide/ports.html
  31. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Bridge Street

Available ports (and non-ports) for non-Unix platforms

   If  a program is derived from XTide source code, I call it a port.  If
   a program contains no XTide source code but can use the same harmonics
   files that some version of XTide did, I call it a non-port.  These are
   only listed if there is no good port to a given platform.  This is not
   an  attempt to track all tide-predicting software, only that with some
   commonality  with  XTide.   Better  software having nothing to do with
   XTide may be available, but is not listed here.

   These  programs  are  all maintained by different people.  They may be
   significantly  different from XTide 2 as documented here.  If you have
   problems   with  a  port  or  non-port,  please  contact  the  correct
   maintainer.   I  cannot  help  with  anything  but  the canonical Unix
   distribution.

  Microsoft Windows

   XTide  can  be  compiled and run using [5]Cygwin, which is an emulated
   Unix  environment  for Windows that is free for typical non-commercial
   users.   The  Cygwin  distribution  and  its  full  license  terms are
   available   from   [6]http://www.cygwin.com/.   Please  refer  to  the
   [7]Installation  section  for  special  instructions about using XTide
   under Cygwin.

   The  latest  "native"  port to Windows, [8]WTides by Phil Thornton, is
   based  on  XTide 2 but contains significant enhancements.  A "nagware"
   binary is available for downloading; sources are available for a fee.

   Caution:   There  have  been  several accusations that Mr. Thornton is
   violating the GNU General Public License and even some ire directed at
   me for having linked to his site.  Firstly, please note that a link is
   not an endorsement.  Secondly, the requirement for "equivalent access"
   to source code that is characterized in the [9]GPL FAQ is ambiguous in
   GPLv2,  under  which XTide was originally released.  It is unambiguous
   in [10]GPLv3, 2nd discussion draft (which is the status of GPLv3 as of
   2007-02-01).

   There  are  two older "native" ports to Microsoft Windows, distributed
   with both sources and binary:
     * The newer older port, "WXTide32" by Mike Hopper, is based on XTide
       1.6.2  but  includes  its  own  location  chooser.  It works under
       Windows   95   or   Windows   NT.    It   has   a   web   page  at
       [11]http://www.wxtide32.com/.
     * The  older older port, "WTide16" and "WTide32" by Paul C. Roberts,
       was  originally  based  on  XTide  1.3  but  may have been updated
       somewhat.   It  works  under Windows 3.1 or Windows 95.  It can be
       found at [12]ftp://ftp.demon.co.uk/pub/ibmpc/win3/apps/wtide.

  Mac

   XTide  should  compile  cleanly  and run under Mac OS 10.3.3 or later.
   See the [13]installation instructions for details.

   Lee  Ann  Rucker has done a nativized port to OS X using [14]Cocoa and
   Objective-C.  It is available at
   [15]http://homepage.mac.com/lrucker/XTide/.

   For  some earlier versions of Mac OS, there is a GPL'd non-port called
   Mr. Tides that you can find at
   [16]http://homepage.mac.com/augusth/MrTides/index.html.

  Palm

   Palm

   [17]Walt Bilofsky has implemented [18]Tide Tool for the Palm Pilot or
   any other compatible device running PalmOS.  Judging from the picture
   it does produce output comparable to that of XTide.

   Bilofsky writes: "Tide Tool used to qualify as a port, and still has a
   modest amount of code from XTide 1.5.  But since Jeff Dairiki redid
   the algorithm to use integer math, I'm not sure how much of it is
   XTide any more.  I guess I'd call it the descendant of a port."

  Pocket PC / Windows CE

   PocketPC

   Dave Buchholz has implemented [19]cTide for the PocketPC 2000 or
   PocketPC 2002.  It's a port of a port ([20]WXTide32), but the
   screenshots still look a lot like XTide.  You can find it at
   [21]http://airtaxi.net/ctide/.

  Timex Datalink USB

   Timex Datalink with DTide

   Paulo Marques has implemented DTide for the Timex Datalink USB
   wristwatch.  It uses a patched version of WXTide32 on the PC to allow
   the user to select locations and prepare simplified harmonics data to
   feed the application on the watch.  It can store more than 200
   (simplified) locations in the watch's memory.  The application on the
   watch is an assembly language non-port using only integer math.

   To get the application, download TreeBrowser_vX.zip and Tree Browser
   Feeders/DTide.zip from the Files > WristApps archive of Yahoo Group
   [22]timexdatalinkusb.

   To get the source (TreeBrowser asm and patch against WXTide32),
   download TreeBrowser_src.zip and DTide_src.zip from the Files >
   WristApps archive of Yahoo Group [23]timexdatalinkusbdevelop.

  HP Calculator

   HP Calculator

   David MacCuish and Dennis Straley have done a similar-in-spirit
   non-port for HP48G and HP49G series calculators.  As of 2001-11-08,
   [24]HpTide is still in development, but it now supports a larger
   number of locations.  For current news and status, please see the
   HpTide web site, [25]http://heygus.2y.net/hptide.
     _________________________________________________________________

   [26]<- Previous [27]-> Next [28]Contents

References

   1. http://www.flaterco.com/xtide/installation.html
   2. http://www.flaterco.com/xtide/modes.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.cygwin.com/
   6. http://www.cygwin.com/
   7. http://www.flaterco.com/xtide/installation.html#cygwin
   8. http://www.wtides.com/
   9. http://www.fsf.org/licensing/licenses/gpl-faq.html#DoesTheGPLAllowDownloadFee
  10. http://gplv3.fsf.org/gpl-draft-2006-07-27.html
  11. http://www.wxtide32.com/
  12. ftp://ftp.demon.co.uk/pub/ibmpc/win3/apps/wtide/
  13. http://www.flaterco.com/xtide/installation.html#mac
  14. http://developer.apple.com/cocoa/
  15. http://homepage.mac.com/lrucker/XTide/
  16. http://homepage.mac.com/augusth/MrTides/index.html
  17. http://www.toolworks.com/bilofsky/
  18. http://www.toolworks.com/bilofsky/tidetool/
  19. http://airtaxi.net/ctide/
  20. http://www.wxtide32.com/
  21. http://airtaxi.net/ctide/
  22. http://tech.groups.yahoo.com/group/timexdatalinkusb/
  23. http://tech.groups.yahoo.com/group/timexdatalinkusbdevelop/
  24. http://heygus.2y.net/hptide
  25. http://heygus.2y.net/hptide
  26. http://www.flaterco.com/xtide/installation.html
  27. http://www.flaterco.com/xtide/modes.html
  28. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Morning in OC

Modes

   This  page  provides an overview of the kinds of things that XTide can
   do.  How to do them will be explained in the [5]next section.

  Graph mode

   San Francisco graph

   Graph  mode gives you a plot of the water level (or water velocity, in
   the case of currents) versus time.  The times of high and low tide (or
   max flood and max ebb) are printed across the top.  Sunrise and sunset
   are  denoted  with different background colors; moonrise, moonset, and
   moon  phases  are  shown  along  the  bottom.   A  + mark on the graph
   indicates the conditions at the time that the graph was generated.

   For  currents,  the  times  of [6]slack water are also shown along the
   bottom.   If  necessary,  crowding  of  the bottom caption line can be
   relieved in several ways (see [7]Advanced usage).

   San Francisco Current graph

  Clock mode

   Clock mode

   Clock mode is similar to graph mode, but the captions are different
   and the window is automatically updated once a minute to show the
   latest conditions.  From top to bottom, the window shows the current
   time, the next high tide (or maximum flood), the predicted height or
   velocity for the current time (shown with a +), and the next low tide
   (or maximum ebb).  Other events like slack water and moon phases do
   not appear.

   Classic analog tide clock If a tide clock is iconified using an
   ancient window manager like twm, the icon will appear as a classic
   round tide clock that gives a vague idea of where you are in the tide
   cycle.  Unfortunately, this feature is not accessible at all from
   newer windows environments that disregard the old icon protocol.  Even
   some of the old window managers had trouble with it; they would crash,
   or the icon would fail to update.

  Plain mode

   Plain text listing of events, no foo-foo.
San Francisco, California
37.8067° N, 122.4650° W

2003-02-13  2:17 PM PST   Moonrise
2003-02-13  3:25 PM PST  -0.32 feet  Low Tide
2003-02-13  5:46 PM PST   Sunset
2003-02-13 10:49 PM PST   4.64 feet  High Tide
2003-02-14  3:05 AM PST   3.16 feet  Low Tide
2003-02-14  5:44 AM PST   Moonset
2003-02-14  7:01 AM PST   Sunrise
2003-02-14  9:02 AM PST   6.27 feet  High Tide

  Calendar mode

   Calendar  mode arranges most of the information available in text mode
   into a commonly used tabular layout.

                                January 2007

   Day High
   Low High
   Low High
   Phase Sunrise Sunset Moonrise Moonset
   Mon 01 3:48 AM EST 0.17 m 9:58 AM EST -0.14 m 5:07 PM EST 0.43 m 7:26
   AM EST 4:53 PM EST 2:49 PM EST 5:49 AM EST
   Tue  02  12:25  AM EST -0.01 m 4:46 AM EST 0.16 m 10:52 AM EST -0.14 m
   6:00 PM EST 0.42 m 7:26 AM EST 4:54 PM EST 3:48 PM EST 6:54 AM EST
   Wed  03  1:15  AM  EST -0.01 m 5:40 AM EST 0.17 m 11:45 AM EST -0.14 m
   6:50  PM EST 0.41 m Full Moon 7:26 AM EST 4:55 PM EST 4:54 PM EST 7:49
   AM EST
   Thu  04  2:00  AM  EST -0.01 m 6:32 AM EST 0.18 m 12:37 PM EST -0.13 m
   7:37 PM EST 0.39 m 7:26 AM EST 4:56 PM EST 6:03 PM EST 8:34 AM EST
   Fri 05 2:42 AM EST -0.00 m 7:20 AM EST 0.19 m 1:28 PM EST -0.12 m 8:21
   PM EST 0.37 m 7:26 AM EST 4:57 PM EST 7:10 PM EST 9:09 AM EST
   Sat 06 3:20 AM EST -0.00 m 8:08 AM EST 0.20 m 2:16 PM EST -0.10 m 9:02
   PM EST 0.35 m 7:26 AM EST 4:58 PM EST 8:15 PM EST 9:37 AM EST
   Sun 07 3:56 AM EST -0.00 m 8:56 AM EST 0.21 m 3:04 PM EST -0.08 m 9:40
   PM EST 0.32 m 7:26 AM EST 4:59 PM EST 9:17 PM EST 10:02 AM EST

   "Alt" calendar mode arranges the information into a traditional weekly
   calendar layout.

                     Sun 07     Mon 08 Tue 09 Wed 10 Thu 11 Fri 12 Sat 13
   Low Tide -0.00 m
   3:56 AM EST
   Sunrise
   7:26 AM EST
   High Tide 0.21 m
   8:56 AM EST
   Moonset
   10:02 AM EST
   Low Tide -0.08 m
   3:04 PM EST
   Sunset
   4:59 PM EST
   Moonrise
   9:17 PM EST
   High Tide 0.32 m
   9:40 PM EST Low Tide -0.01 m
   4:28 AM EST
   Sunrise
   7:26 AM EST
   High Tide 0.22 m
   9:46 AM EST
   Moonset
   10:23 AM EST
   Low Tide -0.05 m
   3:53 PM EST
   Sunset
   5:00 PM EST
   High Tide 0.30 m
   10:16 PM EST
   Moonrise
   10:17 PM EST Low Tide -0.02 m
   4:58 AM EST
   Sunrise
   7:26 AM EST
   High Tide 0.22 m
   10:39 AM EST
   Moonset
   10:43 AM EST
   Low Tide -0.01 m
   4:46 PM EST
   Sunset
   5:00 PM EST
   High Tide 0.27 m
   10:51 PM EST
   Moonrise
   11:16 PM EST Low Tide -0.04 m
   5:28 AM EST
   Sunrise
   7:25 AM EST
   Moonset
   11:03 AM EST
   High Tide 0.24 m
   11:35 AM EST
   Sunset
   5:01 PM EST
   Low Tide 0.03 m
   5:49 PM EST
   High Tide 0.24 m
   11:27 PM EST Moonrise
   12:14 AM EST
   Low Tide -0.06 m
   6:00 AM EST
   Sunrise
   7:25 AM EST
   Last Quarter
   7:45 AM EST
   Moonset
   11:23 AM EST
   High Tide 0.25 m
   12:32 PM EST
   Sunset
   5:02 PM EST
   Low Tide 0.05 m
   7:01 PM EST High Tide 0.21 m
   12:07 AM EST
   Moonrise
   1:15 AM EST
   Low Tide -0.08 m
   6:35 AM EST
   Sunrise
   7:25 AM EST
   Moonset
   11:46 AM EST
   High Tide 0.28 m
   1:29 PM EST
   Sunset
   5:04 PM EST
   Low Tide 0.06 m
   8:18 PM EST High Tide 0.18 m
   12:52 AM EST
   Moonrise
   2:17 AM EST
   Low Tide -0.09 m
   7:15 AM EST
   Sunrise
   7:25 AM EST
   Moonset
   12:14 PM EST
   High Tide 0.30 m
   2:22 PM EST
   Sunset
   5:05 PM EST
   Low Tide 0.06 m
   9:30 PM EST

   Calendar mode is not available from the interactive client.

  Banner mode

   Banner  mode  is  a  specialization  of  graph  mode for output on old
   tractor  feed dot matrix or line printers that use continuous reams of
   paper.   Also useful as a workaround if your printing application does
   stupid things with color graphs.  The graph is turned sideways and the
   aspect  ratio  is adjusted for Pica type.  This mode is only available
   in the command line client.
San Francisco, San Francisco Bay, California
37.8067° N, 122.4650° W

-11****-****-****-***********************
*******3****2****1****0*****1****2****3    4    5    6    7     8    9
******* **** **** **** ***** **** **
-12****f****f****f****f*****f****f    f    f    f    f    f     f    f
*******t****t****t****t*****t**  t    t    t    t    t    t     t    t
*****************************
**************************+ |    |    |    |    |    |    |     |    |
-1************************  |    |    |    |    |    |    |     |    |
****Moonrise************    |    |    |    |    |    |    |     |    |
-***1:55 PM PST********     |    |    |    |    |    |    |     |    |
-2*********************     |    |    |    |    |    |    |     |    |
**********************|     |    |    |    |    |    |    |     |    2007-02-27
**********************|     |    |    |    |    |    |    |     |   2:56 PM PST
-3********************|     |    |    |    |    |    |    |     |    |
**********************|     |    |    |    |    |    |    |     |    |
***********************     |    |    |    |    |    |    |     |    |
-4*********************     |    |    |    |    |    |    |     |    |
************************    |    |    |    |    |    |    |     |    |
*************************   |    |    |    |    |    |    |     |    |
-5************************* |    |    |    |    |    |    |     |    |
****************************|    |    |    |    |    |    |     |    |
******************************   |    |    |    |    |    |     |    |
-6******************************·|····|····|····|····|····|·····|····|·········
**********************************····|····|····|····|····|·····|····|·········
***********************************···|····|····|····|····|·····|····|·········
-7***********************************·|····|····|····|····|·····|····|·········
***************************************····|····|····|····|·····|····|·········
*****************************************··|····|····|····|·····|····|·········
-8*****************************************|····|····|····|·····|····|·········
*********************************************···|····|····|·····|····|·········
**********************************************··|····|····|·····|····|·········
-9*********************************************·|····|····|·····|····|·········
************************************************|····|····|·····|····|·········
*************************************************····|····|·····|····2007-02-27
-10**********************************************····|····|·····|··10:06 PM PST
*************************************************····|····|·····|····|·········
************************************************|····|····|·····|····|·········
-11*********************************************|····|····|·····|····|·········
***********************************************·|····|····|·····|····|·········
-*********************************************··|····|····|·····|····|·········
-12******************************************···|····|····|·····|····|·········
-******************************************|····|····|····|·····|····|·········
******************************************·|····|····|····|·····|····|·········
-1***************************************··|····|····|····|·····|····|·········
****************************************···|····|····|····|·····|····|·········
***************************************····|····|····|····|·····|····|·········
-2*************************************····|····|····|····|·····|····|·········
**************************************|····|····|····|····|·····|····2007-02-28
**************************************|····|····|····|····|·····|···2:45 AM PST
-3************************************|····|····|····|····|·····|····|·········
**************************************|····|····|····|····|·····|····|·········

  Stats mode

   Stats  mode is mainly for finding the highest high tide and lowest low
   tide  within  some  period  of  time.   However,  it  also provides an
   estimation  of  the  Mean Lower Low Water datum based on the generated
   predictions.   In cases where an authoritative benchmark for a station
   is   not   available,   this  can  be  used  to  derive  a  reasonable
   approximation.   If  the datum for the station has already been set to
   MLLW  (as  it  should  have  been,  for  all  U.S.  stations) then the
   estimated value should be close to zero.

   Stats mode is only available in the command line client.
Bar Harbor, Frenchman Bay, Maine
44.3917° N, 68.2050° W

Mathematical upper bound:  15.21 feet
Mathematical lower bound:  -3.87 feet
Mathematical mean, assuming symmetry:   5.67 feet

Searched interval from 2007-01-01 12:00 AM EST to 2008-01-01 12:00 AM EST
Maximum was  13.44 feet at 2007-11-25 10:31 AM EST
Minimum was  -2.05 feet at 2007-04-18  5:53 AM EDT
Mean of maxima and minima was   5.67 feet
Estimated MLLW:   0.15 feet

CPU time used:  0.167974 s

  Raw mode

   Raw  mode  is for getting machine-readable output that can be fed into
   other  Unix  programs.   The  first  column is a Unix time_t timestamp
   (seconds  since  1970-01-01 00:00Z); the second column is tide heights
   in whatever units were selected for the location.
896624777 0.180580
896628377 1.271889
896631977 3.463100
896635577 6.084148
896639177 8.402840
896642777 9.943272
896646377 10.421064
896649977 9.672793
896653577 7.856022
896657177 5.543402
896660777 3.413487
896664377 1.926805
896667977 1.371479

  Medium rare mode

   Medium  rare mode is just like raw mode except that the timestamps are
   "cooked"  according  to  the date and time format settings that are in
   effect.
2002-02-06  4:56 PM EST 2.054437
2002-02-06  5:56 PM EST 1.573781
2002-02-06  6:56 PM EST 1.086896
2002-02-06  7:56 PM EST 0.656111
2002-02-06  8:56 PM EST 0.224729
2002-02-06  9:56 PM EST -0.161049
2002-02-06 10:56 PM EST -0.265521
2002-02-06 11:56 PM EST 0.077530

  List mode

   List  mode  does  not provide tide predictions at all.  It is simply a
   way  to  get  the  list  of  supported locations from the command line
   client.

   The  'Type'  column  shows  Ref  for  reference  stations  and Sub for
   subordinate stations.  [8]You should care about the difference.

   Location Type Coordinates
   0.8 n.mi. above entrance, Alloway Creek, New Jersey Sub 39.4967° N,
   75.5167° W
   130th Street, Hudson River, New York Sub 40.8167° N, 73.9667° W
   2.5  miles  above mouth, Little Satilla River, Georgia Sub 31.0583° N,
   81.4933° W
   2.5  n.mi.  above  entrance, Alloway Creek, New Jersey Sub 39.5050° N,
   75.4833° W
   3  miles  above  A1A  highway  bridge,  Loxahatchee River, Florida Sub
   26.9700° N, 80.1267° W
   37th  Avenue,  Long  Island  City,  East River, New York, New York Sub
   40.7617° N, 73.9467° W

  About mode

   About  mode  does  not  provide  tide predictions either.  Instead, it
   shows the metadata for a station ("About this station").

   Name              
Eastport, Passamaquoddy Bay, ME

   In file           
harmonics-dwf-2004-10-18-v2.tcd

   Station ID context
NOS

   Station ID        
8410140

   Date imported     
2004-09-01

   Coordinates       
44.9033° N, 66.9850° W

   Country           
U.S.A.

   Time zone         
:America/New_York

   Source            
http://tidesandcurrents.noaa.gov/

   Restriction       
Public domain

   Comments
Harmonic constants from web snapshot taken 2004-08-26
Datum from benchmark sheet, publication date 2003-04-21

   Type              
Reference station, tide

   Meridian          
0:00

   Datum             
Mean Lower Low Water

   Native units      
meters

   Confidence        
10

Formats

   XTide  can render output in seven different formats:  X-windows, HTML,
   LaTeX, iCalendar, PNG, CSV, or text.  The X-windows format is implicit
   in  the  interactive  client  and  can't  be selected explicitly.  The
   others  can  be selected in the non-interactive client and are invoked
   automatically  by  the the interactive and web clients (e.g., when you
   save output to a file).

   The  currently  supported  combinations  of  mode  and  format  are as
   follows:

         Mode                 Legal forms
     about         text, HTML, X-windows
     banner        text
     calendar      text, HTML, LaTeX, iCalendar, CSV
     alt. calendar text, HTML, LaTeX
     clock         PNG, X-windows
     graph         text, PNG, X-windows
     list          text, HTML
     plain         text, X-windows, CSV
     raw           text, X-windows, CSV
     medium rare   text, X-windows, CSV
     stats         text

   The  HTML  and PNG formats are adequately demonstrated by the examples
   above in the Modes section.

  Text format

   Several  of  the  preceding  examples,  like  plain mode, were in text
   format.  Here is an example of graph mode using the text format:
·················San Francisco, San Francisco Bay, California            ······
-12·····2003-02-13·············2003-02-13                 2003-02-13     ······
 PST····2:18 AM PST············8:12 AM PST                3:25 PM PST    ······
································                                         ······
································                                         ······
································                                         ······
································                                         ······
2 m·---------------------------------------------------------------------------
·····························*************                               ······
··························******************                             ······
***···················************************                           ······
**********·······*******************************                         ······
1 m***********************************************-----------------------------
****************************************************                     ·····*
******************************************************                   ···***
********************************************************                 ******
**********************************************************            *********
0 m****************************************************************************
*******************************************************************************
*******************************************************************************
********************Moonset****************************Moonrise****************
******************4:51 AM PST*************************2:17 PM PST**************
1**12***1***2***3**4***5***6***7***8***9*10**11**12***1***2***3***4**5***6***7*
|**|||**|***|***|**|***|***|***|***|***|**|***|***|***|***||**|***|**|***|***|*

   Calendar mode is kind of cramped in text format if you use all default
   settings,  but  it can be made to work by using a compact time format,
   setting   a   wider  TTY  width,  and/or  turning  off  sun  and  moon
   information.   These  are  [9]settings  that  you  can change with the
   [10]control  panel  or  [11]command-line switches.  See [12]Appendix C
   for related discussion.
Bar Harbor, Frenchman Bay, Maine
44.3917° N, 68.2050° W

                                   May 2006

Day    High   Low    High   Low    High   Phase  Sunris Sunset Moonri Moonse
Mon 01 01:42  08:10  14:23  20:23                05:23  19:36  07:38
Tue 02 02:32  09:02  15:16  21:16                05:22  19:37  08:38  00:32
Wed 03 03:25  09:56  16:10  22:12                05:20  19:39  09:44  01:17
Thu 04 04:21  10:52  17:07  23:12                05:19  19:40  10:51  01:52
Fri 05 05:20  11:49  18:05                First  05:18  19:41  11:58  02:19
Sat 06        00:13  06:20  12:45  19:01         05:16  19:42  13:03  02:40
Sun 07        01:11  07:18  13:38  19:52         05:15  19:44  14:07  02:59
Mon 08        02:06  08:12  14:26  20:39         05:14  19:45  15:10  03:15
Tue 09        02:55  09:01  15:10  21:21         05:12  19:46  16:14  03:31
Wed 10        03:39  09:46  15:51  21:59         05:11  19:47  17:19  03:47
Thu 11        04:21  10:27  16:28  22:36         05:10  19:48  18:27  04:05
Fri 12        04:59  11:06  17:05  23:11         05:09  19:49  19:38  04:26
Sat 13        05:36  11:45  17:41  23:48  Full M 05:07  19:51  20:51  04:52
Sun 14        06:15  12:24  18:19                05:06  19:52  22:02  05:26
Mon 15 00:26  06:55  13:05  18:59                05:05  19:53  23:07  06:11
Tue 16 01:08  07:38  13:49  19:44                05:04  19:54         07:08
Wed 17 01:55  08:25  14:38  20:35                05:03  19:55  00:02  08:17
Thu 18 02:46  09:18  15:32  21:32                05:02  19:56  00:45  09:34
Fri 19 03:43  10:14  16:30  22:34                05:01  19:57  01:19  10:53
Sat 20 04:45  11:13  17:30  23:40         Last Q 05:00  19:58  01:46  12:12
Sun 21 05:50  12:14  18:31                       04:59  19:59  02:08  13:30
Mon 22        00:46  06:56  13:14  19:31         04:58  20:00  02:29  14:47
Tue 23        01:50  07:59  14:12  20:27         04:57  20:01  02:49  16:05
Wed 24        02:49  08:59  15:07  21:21         04:56  20:02  03:10  17:23
Thu 25        03:45  09:56  15:59  22:12         04:56  20:03  03:34  18:43
Fri 26        04:38  10:49  16:49  23:00         04:55  20:04  04:03  20:01
Sat 27        05:28  11:39  17:38  23:48  New Mo 04:54  20:05  04:40  21:15
Sun 28        06:16  12:27  18:25                04:53  20:06  05:26  22:18
Mon 29 00:34  07:03  13:15  19:13                04:53  20:07  06:23  23:09
Tue 30 01:21  07:51  14:03  20:01                04:52  20:08  07:27  23:49
Wed 31 02:09  08:38  14:51  20:50                04:52  20:09  08:35

  LaTeX format

   Running  LaTeX  formatted  output  through  pdflatex yields a PDF that
   looks  approximately  [13]like  this.  See [14]Appendix C for hints on
   obtaining the best results.

  iCalendar format

   The  iCalendar  format  yields  an  .ics  file that can be imported by
   standards-compliant   calendar  tools  to  put  tide  events  on  your
   schedule.  It is only useful in calendar mode.

  CSV format

   CSV  stands  for Comma-Separated Values, a.k.a. comma-delimited.  This
   rigid  format  is  useful for importing XTide output into database and
   spreadsheet  applications with fixed columns.  Commas that are part of
   field values are replaced by the pipe character (|).
Washington| D.C.,2004-03-04,3:40 PM EST,,Moonrise
Washington| D.C.,2004-03-04,6:04 PM EST,,Sunset
Washington| D.C.,2004-03-04,6:23 PM EST,2.75 ft,High Tide
Washington| D.C.,2004-03-05,1:30 AM EST,0.21 ft,Low Tide

   In calendar mode, the columns in CSV format are:  location name, date,
   five  reps  of  (max  time,  max  value),  five reps of (min time, min
   value),  ten  reps  of slack time, sunrise, sunset, moonrise, moonset.
   The  number  of  columns  allocated  is controlled by the compile-time
   constants   numMaxMin  and  numRiseSet  in  CalendarFormC.cc.   Events
   exceeding  the  number  of  columns  available  are  discarded  with a
   warning.  Moon phases and mark level crossings are just discarded.

   The  use  of  compile-time  constants  instead of dynamically adjusted
   values  is  intentional, since whatever application is reading the CSV
   output   needs  the  interpretation  of  columns  to  be  predictable.
   However,  the  default  configuration allowing one column for rise and
   set  events is not always adequate.  Yes!  You can have two sunsets in
   one day, and you don't even need Daylight Savings Time to do it:
Isla Neny, Antarctica
68.2000° S, 67.0000° W

2001-01-24 12:03 AM ARST   Sunset
2001-01-24  3:17 AM ARST   Sunrise
2001-01-24 11:57 PM ARST   Sunset
     _________________________________________________________________

   [15]<- Previous [16]-> Next [17]Contents

References

   1. http://www.flaterco.com/xtide/ports.html
   2. http://www.flaterco.com/xtide/interactive.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/interactive.html
   6. http://www.flaterco.com/xtide/faq.html#240
   7. http://www.flaterco.com/xtide/advanced.html#crowding
   8. http://www.flaterco.com/xtide/faq.html#refsub
   9. http://www.flaterco.com/xtide/settings.html
  10. http://www.flaterco.com/xtide/advanced.html#cp
  11. http://www.flaterco.com/xtide/settings.html
  12. http://www.flaterco.com/xtide/pound_to_fit.html
  13. http://www.flaterco.com/xtide/BarHarbor.pdf
  14. http://www.flaterco.com/xtide/pound_to_fit.html
  15. http://www.flaterco.com/xtide/ports.html
  16. http://www.flaterco.com/xtide/interactive.html
  17. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Pemaquid bell

Using the interactive interface

   The  first  time  you run xtide, you will get a license and disclaimer
   window.  Read it, then click "Don't show this again" and dismiss it.

   When  XTide  is  finished  indexing the harmonics files you will get a
   location  chooser.   The location chooser initially shows a hemisphere
   of the globe.  The location list enumerates every tide station that is
   plotted  on the map.  Buttons with labels such as "A-S" and "S-Z" will
   appear  on the location list window if the list is too long to display
   all  at once; use these buttons to switch between the different pieces
   of the list.

   (If  you  do  not  get  outlines  of  coastlines,  please refer to the
   [5]installation section regarding World Vector Shoreline files.)

   Globe window

   Location list window

   You can change to a flat map projection that shows the entire world at
   once  by  clicking  on  Flat.  You can make this your default location
   chooser if desired (see the later section [6]Customizing XTide).

   Map window

   You  can zoom in on an area by clicking on the map with the left mouse
   button;  zooming  out is accomplished with the button at the bottom of
   the  map  window.   Your  view can be shifted left, right, up, or down
   using  the  arrow  keys on the keyboard.  The location list updates to
   contain  only those tide stations that are visible.  You can cause the
   location  list  to include all available locations at once by clicking
   on  List All.  This will also bring up locations whose coordinates are
   unknown.

   Instead  of  zooming,  you  can  narrow  the  list  to a small area by
   clicking  on  that area with the right mouse button.  A circle will be
   drawn on the map indicating the area selected:

   Map window with circle

   When you are ready to choose a location, you can either click on it in
   the  location  list  or  zoom  down  to it on the map and click on the
   appropriate  red  dot  with the middle mouse button.  A tide graph for
   the selected location will then pop up.

   Graph window

   The Backward and Forward buttons allow you to move forward or backward
   in  time by a small amount.  Pull down the Options menu to gain access
   to  the  Set  Time option, which allows arbitrarily large adjustments.
   The Options menu also provides these other options:

   Option Function
   Save Export the contents of the window to a PNG or text file, as
   appropriate.  (In raw and medium rare modes, you are given the
   opportunity to adjust the start and end times for the output.)
   Set Mark See [7]next section.
   Convert ft<->m Convert units to the preferred system.
   Set Aspect See [8]next section.
   Set Step See [9]next section.
   New Graph Window Pop up a graph mode window for the location.
   New Plain Mode Window Pop up a plain mode window for the location.
   New Raw Mode Window Pop up a raw mode window for the location.
   New  Medium  Rare Mode Window Pop up a medium rare mode window for the
   location.
   New Clock Window Pop up a clock mode window for the location.
   About This Station Show station metadata.
   New Location Chooser Pop up a new location chooser.
   Control Panel See [10]next section.

   Without  getting  into  the complicated options, you can navigate from
   the  location  chooser  to  a graph window to other modes for the same
   location  as  you  see  fit.   Use  the  Dismiss buttons to get rid of
   windows that you are through with.

   Text window

   Text windows provide Forward and Backward buttons for scrolling
   forward and backward in time, and they also provide the same Options
   menu that is available on graph windows.

   Note:  Starting with XTide 2.9, text windows support mouse wheel
   scrolling provided that the mouse wheel has been mapped to buttons 4
   and 5.  This mapping is typically configured in xorg.conf (Option
   "ZAxisMapping" "4 5").

   Clock window   Clock window with buttons

   By default, clock windows first appear with no buttons whatsoever,
   which is how you want them if you are going to leave them running on
   your desktop.  However, you can make the buttons appear and disappear
   by clicking anywhere on the graph inside of the clock window.

   The Options menu is again the same.  Forward and Backward buttons are
   not provided for the obvious reason.
     _________________________________________________________________

   [11]<- Previous [12]-> Next [13]Contents

References

   1. http://www.flaterco.com/xtide/modes.html
   2. http://www.flaterco.com/xtide/advanced.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/installation.html#WVS
   6. http://www.flaterco.com/xtide/settings.html
   7. http://www.flaterco.com/xtide/advanced.html
   8. http://www.flaterco.com/xtide/advanced.html
   9. http://www.flaterco.com/xtide/advanced.html
  10. http://www.flaterco.com/xtide/advanced.html
  11. http://www.flaterco.com/xtide/modes.html
  12. http://www.flaterco.com/xtide/advanced.html
  13. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]The tide cometh, Provincetown, MA

Advanced usage

  Mark level

   The  "mark  level"  is  a specific tidal height or current velocity of
   your choosing.  When you set a mark level for a location, the times at
   which  the  tide level crosses the mark level will be displayed at the
   bottom  of  graphs and included in plain listings and calendars.  This
   option  is  useful  to  determine  the times when the tide will be low
   enough  to  expose  something  that  is submerged at high tide or high
   enough  to  provide  a  desired  depth.   You  can set a mark level by
   selecting  the  Set Mark option on the Options menu.  In the following
   example,  a  mark  level  of  1  m  has  been  applied  to  Bar Harbor
   predictions  to find the approximate time at which one can walk to Bar
   Island without getting one's feet wet.

   Bar Harbor with mark level

   Mark  level  crossings  are not displayed in clock mode windows due to
   lack of space.

  Aspect

   The  "aspect" is a number that controls how stretched out or scrunched
   up  a  graph  is.  If timestamps are overlapping one another on a tide
   graph  and  becoming  unreadable,  you can increase the aspect to make
   them  farther  apart.   An aspect of 1.0 is "normal;" an aspect of 2.0
   stretches  the  graph  by  a  factor  of  2; an aspect of 0.5 does the
   opposite,  compressing  the  graph.   You  can  change  the  aspect by
   selecting the Set Aspect option on the Options menu.

  Step

   In  raw and medium rare modes, tide levels are normally listed with an
   increment  of one hour for successive lines of output.  You can adjust
   this increment using the Set Step option.

  The control panel

  The control panel is the easiest way to customize the many user-serviceable
  [5]settings of XTide.  It's not pretty, but it gets the job done.

  XTide control panel

  Colors can be changed to any of the "standard" X-windows color names or to
  24-bit RGB specifications of the form rgb:hh/hh/hh by typing the new colors
  in the dialog boxes.  Other settings have pull-down choice menus or counting
  buttons to help you along.  Least user-friendly, but most powerful, are the
  timestamp formats.  In return for reading the Unix man page for the strftime
  library function, you are empowered to change the timestamp formats to
  practically anything you could ever need.

  You can choose Apply to see how the settings look in the current session
  only, or Save to make the settings permanent.  They will be saved in the file
  ~/.xtide.xml.
  Example 1:  Three ways to fix crowding of the bottom caption line

  Original graph with crowded caption line:

  San Francisco Current graph

  With aspect 1.25 (to stretch out the graph):

  San Francisco Current graph

  With time format "%H:%M" (to eliminate AM/PM and time zone verbiage):

  San Francisco Current graph

  With event mask "Mm" (to filter out moonrise and moonset events):

  San Francisco Current graph
  Example 2:  Two ways to fix missing depth axis

  This station has such a small tidal range that the only label on the depth
  axis is zero meters, which is kind of useless:

  Missing depth example

  With option to label tenths of units enabled:

  Missing depth example

  With preferred units set to feet:

  Missing depth example
  Command line options

  The interactive client supports all of the command line switches related to
  [6]settings which are described in a later section.  In addition, it supports
  the following.

   -b "YYYY-MM-DD HH:MM"
          With -l, specify the begin (start) time for predictions using
          the ISO 8601 compliant format YYYY-MM-DD HH:MM, where hours
          range from 00 to 23.  The timestamp is in the local time zone
          for the location, or in UTC if the -z setting is engaged.  If
          no -b is supplied, the current time will be used.  (Note
          [7]Quirk #1)

   -display "X display"
          Specify the X display, e.g. "quake:0.0".  This overrides the
          DISPLAY environment variable.

   -fn "font"
          Specify the font to use for text windows, buttons, and labels.
          This will not affect the font used in tide graphs and other
          cramped spaces, which is not a user-selectable parameter.

   -geometry "±XOFF±YOFF"
          Specify a position for the window corresponding to the first
          use of -l.  (Width and height are controlled by different
          [8]settings.)

   -l "Location Name"
          Specify a location for tide predictions.  When given to the
          interactive client, this causes it to start a tide clock for
          the specified location instead of launching a location chooser
          on startup.  This is useful for starting a tide clock
          automatically when you log on.  Multiple uses of -l will result
          in multiple tide clocks.

   -m a|g|m|p|r
          With -l, specify mode to be about, graph, medium rare, plain,
          or raw instead of clock.

   -v
          Print version string and exit.  Please note that versions
          marked as DEVELOPMENT versions are not really versioned; they
          are work in progress and will change without warning.

  If you use the same location a lot, you can set the environment variable
  XTIDE_DEFAULT_LOCATION to its name instead of using -l every time.

  Other switches that are supported by the [9]non-interactive interface are not
  supported by the interactive interface and will be ignored.

  The arguments to -display, -fn, and -geometry cannot be concatenated with the
  switches (see [10]Quirk #5).
    ________________________________________________________________________

  [11]<- Previous [12]-> Next [13]Contents

References

   1. http://www.flaterco.com/xtide/interactive.html
   2. http://www.flaterco.com/xtide/tty.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/settings.html
   6. http://www.flaterco.com/xtide/settings.html
   7. http://www.flaterco.com/xtide/bugs.html
   8. http://www.flaterco.com/xtide/settings.html
   9. http://www.flaterco.com/xtide/tty.html
  10. http://www.flaterco.com/xtide/bugs.html
  11. http://www.flaterco.com/xtide/interactive.html
  12. http://www.flaterco.com/xtide/tty.html
  13. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Tide closes in

Using the command line interface

   The  command  line interface, tide, supports a number of [5]modes that
   cannot  be  accessed  with the interactive client.  It can run without
   X-windows, and unlike the interactive client, it can easily be invoked
   from shell scripts.

   The  minimal  usage  is  simply  to  specify  a location with -l.  The
   default mode is plain, and the default format is text:

$ tide -l "anchorage, al"
Anchorage, Alaska
61.2383° N, 149.8883° W

2003-02-12  7:27 AM AKST   Moonset
2003-02-12  8:50 AM AKST   Sunrise
2003-02-12 10:19 AM AKST  10.72 feet  Low Tide
2003-02-12 11:34 AM AKST   Moonrise
2003-02-12  3:42 PM AKST  24.41 feet  High Tide
2003-02-12  5:37 PM AKST   Sunset
2003-02-12 11:00 PM AKST   1.95 feet  Low Tide
2003-02-13  5:31 AM AKST  25.51 feet  High Tide
2003-02-13  8:29 AM AKST   Moonset

   If  you  use  the  same  location  a  lot, you can set the environment
   variable  XTIDE_DEFAULT_LOCATION to its name instead of using -l every
   time.

   The  non-interactive  client supports all of the command line switches
   related  to  [6]settings  which  are described in a later section.  In
   addition, it supports the following.

   -b "YYYY-MM-DD HH:MM"
          Specify  the  begin  (start) time for predictions using the ISO
          8601  compliant format YYYY-MM-DD HH:MM, where hours range from
          00  to  23.   The  timestamp  is in the local time zone for the
          location,  or in UTC if the -z setting is engaged.  If no -b is
          supplied, the current time will be used.  (Note [7]Quirk #1)

   -e "YYYY-MM-DD HH:MM"
          Specify  the end (stop) time for predictions using the ISO 8601
          compliant format YYYY-MM-DD HH:MM, where hours range from 00 to
          23.   The timestamp is in the local time zone for the location,
          or  in UTC if the -z setting is engaged.  If no -e is supplied,
          the  end  time  will  be set to four days after the begin time.
          (Note [8]Quirk #2)

   When it matters, -b and -e ranges mean specifically "all t such that b
   =< t < e."

   -f c|h|i|l|p|t
          Specify  the output format as CSV, HTML, iCalendar, LaTeX, PNG,
          or  text.   See  the [9]modes page for legal modes and formats.
          The default is text.

   -l "Location Name"
          Specify  a  location  for tide predictions.  You can use the -l
          switch   more  than  once  if  you  want  to  specify  multiple
          locations.

   -m a|b|c|C|g|l|m|p|r|s
          Specify  mode  to  be  about,  banner, calendar, alt. calendar,
          graph,  list,  medium  rare,  plain,  raw,  or  stats.  See the
          [10]modes  page  for  legal  modes and formats.  The default is
          plain.

   -ml [-]N.NN(ft|m|kt)
          Specify  the  mark  level  to  be  used  in  predictions.   The
          predictions  will include the times when the tide level crosses
          the mark.  Example usage: -ml -0.25ft

   -o "filename"
          Redirect output to the specified file (appends).

   -s "HH:MM"
          Specify  the  step  interval,  in hours and minutes, for raw or
          medium rare mode predictions.  The default is one hour.

   -v
          Print  version  string  and  exit.   Please  note that versions
          marked  as  DEVELOPMENT versions are not really versioned; they
          are work in progress and will change without warning.

   The  interactive  interface does not support all of these switches and
   options.  For example, you can't pop up a graph with a mark line on it
   by  saying  xtide  -m g -ml 1ft.  Refer to the [11]previous page for a
   list of the options supported by the interactive interface.

   Starting  with  version 2.6, XTide understands the following syntactic
   shortcuts:
     * Arguments can be concatenated with their switches.
     * A yes/no switch that omits its argument implies "y".
     * Using  +xx instead of -xx for a yes/no switch inverts the argument
       (so if the argument is omitted, "n" is implied).

   Some shorthand forms are ambiguous.  For example, -lw5 could mean "set
   the line width to 5" (-lw 5) or it could mean "load the location named
   w5"  (-l w5).  If this happens, you will get an error and will need to
   spell out what you meant.
     _________________________________________________________________

   [12]<- Previous [13]-> Next [14]Contents

References

   1. http://www.flaterco.com/xtide/advanced.html
   2. http://www.flaterco.com/xtide/xttpd.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/modes.html
   6. http://www.flaterco.com/xtide/settings.html
   7. http://www.flaterco.com/xtide/bugs.html
   8. http://www.flaterco.com/xtide/bugs.html
   9. http://www.flaterco.com/xtide/modes.html
  10. http://www.flaterco.com/xtide/modes.html
  11. http://www.flaterco.com/xtide/advanced.html#intopts
  12. http://www.flaterco.com/xtide/advanced.html
  13. http://www.flaterco.com/xtide/xttpd.html
  14. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Nobska Light, Cape Cod, MA, 1998-06-17

Running the web server

   xttpd is an XTide web server.  It provides web-based access to XTide's
   tide  predictions  by  allowing a web browser to speak directly to the
   XTide  program  in  HTTP.   xttpd can replace httpd or it can co-exist
   with   one.    Usage:    xttpd   [port]  [...other  xtide  [5]settings
   switches...].

   xttpd  forks  itself  into the background and uses the syslog facility
   for  all  logging.  Hosts connecting to xttpd are logged with priority
   INFO.

   If  you  run xttpd with no command line arguments, it will assume that
   it  is  replacing  httpd  and  try to bind port 80.  If you want it to
   co-exist  with  an existing server, or if you do not have privilege to
   get  port  80,  give  it  the  port  number  as the first command line
   argument:

% xttpd 8080

   You  will  then  need  to  link it up as http://www.wherever.org:8080/
   instead  of  just  http://www.wherever.org/,  but otherwise, no damage
   done.   Similarly,  if  you  wish  to bind a specific address, you can
   specify that as the first argument:

% xttpd 127.0.0.2

   If  you need to specify both address and port number, separate the two
   with a slash, like this:

% xttpd 127.0.0.2/8080

   Once the port is established, xttpd will try to set its UID and GID to
   values  that  were  specified  at compile time.  If it is unable to do
   this,   it  will  log  failure  messages  to  syslog  and  then  exit.
   Consequently,  if it is to be started by someone other than root, that
   user's  UID  and GID must be configured at compile time.  Instructions
   for doing this are available at
   [6]http://www.flaterco.com/xtide/installation.html#xttpd.

   You  can  set  the  address  for  feedback  either  at compile time as
   described  in  the  installation  instructions or with the environment
   variable XTTPD_FEEDBACK.

   xttpd  will  produce  a small number of zombie processes during normal
   operation.  They are cleaned up after each new connection, so there is
   no cause for concern.

   Since  a  web  site is supposed to be self-explanatory, the process of
   using  xttpd  will not be documented here.  If there are problems with
   people  not  being  able  to figure out how to use it, these should be
   reported  to  me  as  bugs, and the explanatory text in the web server
   will be updated accordingly.

  Troubleshooting

  Q: When I run xttpd, it exits immediately with no errors to tell me what went
  wrong.

  A: When executed, xttpd immediately disassociates itself from your terminal
  and starts logging all diagnostics to syslog.  So look in your system logs.
  You will find these someplace like /var/log or /var/adm/log.
    ________________________________________________________________________

  [7]<- Previous [8]-> Next [9]Contents

References

   1. http://www.flaterco.com/xtide/tty.html
   2. http://www.flaterco.com/xtide/settings.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/settings.html
   6. http://www.flaterco.com/xtide/installation.html#xttpd
   7. http://www.flaterco.com/xtide/tty.html
   8. http://www.flaterco.com/xtide/settings.html
   9. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Girl feeding gulls

Customizing XTide

   XTide is customized by changing its settings.  The most convenient way
   to  do  this is generally through the control panel that is documented
   in a [5]previous section.  However, you can also change these settings
   in  config.hh,  in  your X resources database, or on the command line.
   The  order  of precedence, from least significant to most significant,
   is:
    1. config.hh
    2. Xdefaults (X resources)
    3. ~/.xtide.xml (control panel)
    4. command line

   Note that only xtide (not xttpd or tide) reads Xdefaults.

   Canonically, all command line settings take the form -xx value, with a
   space  between  the  switch  and  the  supplied  value.  The yes-or-no
   settings  get  a  value of "y" or "n".  However, starting with version
   2.6, XTide understands the following syntactic shortcuts:
     * Arguments can be concatenated with their switches.
     * A yes/no switch that omits its argument implies "y".
     * Using  +xx instead of -xx for a yes/no switch inverts the argument
       (so if the argument is omitted, "n" is implied).

   Some shorthand forms are ambiguous.  For example, -lw5 could mean "set
   the line width to 5" (-lw 5) or it could mean "load the location named
   w5"  (-l w5).  If this happens, you will get an error and will need to
   spell out what you meant.

   XTide*antialias
          Anti-alias tide graphs on true color displays? (y/n)
          Default: y
          Command line: -aa
          config.hh: antialias
          .xtide.xml: <xtideoptions aa="y"/>

   XTide*background
          Background color for text windows and location chooser.
          Default: white
          Command line: -bg
          config.hh: bgdefcolor
          .xtide.xml: <xtideoptions bg="white"/>

   XTide*buttoncolor
          Background color of buttons.
          Default: gray80
          Command line: -bc
          config.hh: buttondefcolor
          .xtide.xml: <xtideoptions bc="gray80"/>

   XTide*cbuttons
          Create tide clocks with buttons? (y/n)
          Default: n
          Command line: -cb
          config.hh: cbuttons
          .xtide.xml: <xtideoptions cb="n"/>

   XTide*cwidth
          Default  width for tide clocks.  Note:  Default clock height is
          the same as default graph height (XTide*gheight).
          Default: 84
          Command line: -cw
          config.hh: defcwidth
          .xtide.xml: <xtideoptions cw="84"/>

   XTide*datefmt
          Strftime style format string for printing dates.
          Default: %Y-%m-%d
          Command line: -df
          config.hh: datefmt
          .xtide.xml: <xtideoptions df="%Y-%m-%d"/>

   XTide*datumcolor
          Color of datum line in tide graphs. [[6]*]
          Default: white
          Command line: -Dc
          config.hh: datumdefcolor
          .xtide.xml: <xtideoptions Dc="white"/>

   XTide*daycolor
          Daytime background color in tide graphs.
          Default: SkyBlue
          Command line: -dc
          config.hh: daydefcolor
          .xtide.xml: <xtideoptions dc="SkyBlue"/>

   XTide*ebbcolor
          Foreground in tide graphs during outgoing tide.
          Default: SeaGreen
          Command line: -ec
          config.hh: ebbdefcolor
          .xtide.xml: <xtideoptions ec="SeaGreen"/>

   XTide*eventmask
          Events to suppress (p = phase of moon, S = sunrise, s = sunset,
          M  =  moonrise,  m  = moonset), or x to suppress none.  E.g, to
          suppress  all  sun  and moon events, set eventmask to the value
          pSsMm.
          Default: x
          Command line: -em
          config.hh: eventmask
          .xtide.xml: <xtideoptions em="x"/>

   XTide*extralines
          Draw datum and middle-level lines in tide graphs? (y/n) [[7]*]
          Default: n
          Command line: -el
          config.hh: extralines
          .xtide.xml: <xtideoptions el="n"/>

   XTide*flatearth
          Prefer flat map to round globe location chooser? (y/n)
          Default: n
          Command line: -fe
          config.hh: flatearth
          .xtide.xml: <xtideoptions fe="n"/>

   XTide*floodcolor
          Foreground in tide graphs during incoming tide.
          Default: Blue
          Command line: -fc
          config.hh: flooddefcolor
          .xtide.xml: <xtideoptions fc="Blue"/>

   XTide*font
          Font used for button labels and verbiage in text windows.
          Default: as incoming from X11
          Command line: -fn
          config.hh: N/A
          .xtide.xml: N/A

   XTide*foreground
          Color of text and other notations.
          Default: black
          Command line: -fg
          config.hh: fgdefcolor
          .xtide.xml: <xtideoptions fg="black"/>

   XTide*gaspect
          Default aspect for tide graphs.
          Default: 1.0
          Command line: -ga
          config.hh: defgaspect
          .xtide.xml: <xtideoptions ga="1.0"/>

   XTide*gheight
          Default height for tide graphs.
          Default: 312
          Command line: -gh
          config.hh: defgheight
          .xtide.xml: <xtideoptions gh="312"/>

   XTide*globelongitude
          Default center longitude for location chooser.
          Valid values: -180 -150 -120 -90 -60 -30 0 30 60 90 120 150 360
          360 will pick the longitude with the most tide stations.
          Default: 360
          Command line: -gl
          config.hh: defgl
          .xtide.xml: <xtideoptions gl="360"/>

   XTide*graphtenths
          Label tenths of units in tide graphs? (y/n)
          Default: n
          Command line: -gt
          config.hh: graphtenths
          .xtide.xml: <xtideoptions gt="n"/>

   XTide*gwidth
          Default width for tide graphs.
          Default: 960
          Command line: -gw
          config.hh: defgwidth
          .xtide.xml: <xtideoptions gw="960"/>

   XTide*hourfmt
          Strftime  style  format string for printing hour labels on time
          axis.
          Default: %l
          Command line: -hf
          config.hh: hourfmt
          .xtide.xml: <xtideoptions hf="%l"/>

   XTide*infer
          Use  inferred  values  for  some  constituents.  For expert use
          only.
          Default: n
          Command line: -in
          config.hh: infer
          .xtide.xml: <xtideoptions in="n"/>

   XTide*lwidth
          Width for lines in tide graphs with nofill.
          Default: 2.5
          Command line: -lw
          config.hh: deflwidth
          .xtide.xml: <xtideoptions lw="2.5"/>

   XTide*markcolor
          Color  of  mark  line  in  graphs  and  of location dots on the
          spinning globe.
          Default: red
          Command line: -mc
          config.hh: markdefcolor
          .xtide.xml: <xtideoptions mc="red"/>

   XTide*mslcolor
          Color of middle-level line in tide graphs. [[8]*]
          Default: yellow
          Command line: -Mc
          config.hh: msldefcolor
          .xtide.xml: <xtideoptions Mc="yellow"/>

   XTide*nightcolor
          Nighttime background color in tide graphs.
          Default: DeepSkyBlue
          Command line: -nc
          config.hh: nightdefcolor
          .xtide.xml: <xtideoptions nc="DeepSkyBlue"/>

   XTide*nofill
          Draw tide graphs as line graphs? (y/n)
          Default: n
          Command line: -nf
          config.hh: nofill
          .xtide.xml: <xtideoptions nf="n"/>

   XTide*nosunmoon
          Deprecated.  Use eventmask instead.
          Default: n
          Command line: -ns
          config.hh: N/A (use eventmask)
          .xtide.xml: <xtideoptions ns="n"/>

   XTide*pageheight
          Nominal  length  of  paper  in LaTeX output (mm). This need not
          match  your actual paper; use "Shrink oversized pages" in print
          options.
          Default: 420
          Command line: -ph
          config.hh: defpageheight
          .xtide.xml: <xtideoptions ph="420"/>

   XTide*pagemargin
          Nominal  width  of top, bottom, left and right margins in LaTeX
          output (mm). Actual width will depend on print scaling.
          Default: 10
          Command line: -pm
          config.hh: defpagemargin
          .xtide.xml: <xtideoptions pm="10"/>

   XTide*pagewidth
          Nominal  width  of  paper  in  LaTeX output (mm). This need not
          match  your actual paper; use "Shrink oversized pages" in print
          options.
          Default: 297
          Command line: -pw
          config.hh: defpagewidth
          .xtide.xml: <xtideoptions pw="297"/>

   XTide*timefmt
          Strftime style format string for printing times.
          Default: %l:%M %p %Z
          Command line: -tf
          config.hh: timefmt
          .xtide.xml: <xtideoptions tf="%l:%M %p %Z"/>

   XTide*toplines
          Draw depth lines on top of tide graph? (y/n)
          Default: n
          Command line: -tl
          config.hh: toplines
          .xtide.xml: <xtideoptions tl="n"/>

   XTide*ttyheight
          Height of ASCII graphs (characters).
          Default: 24
          Command line: -th
          config.hh: defttyheight
          .xtide.xml: <xtideoptions th="24"/>

   XTide*ttywidth
          Width of ASCII graphs, banners, and calendars (characters).
          Default: 79
          Command line: -tw
          config.hh: defttywidth
          .xtide.xml: <xtideoptions tw="79"/>

   XTide*units
          Preferred units of length: ft, m, or x (no preference).
          Default: x
          Command line: -u
          config.hh: prefunits
          .xtide.xml: <xtideoptions u="x"/>

   XTide*zulu
          Coerce all time zones to UTC? (y/n)
          Default: n
          Command line: -z
          config.hh: forceZuluTime (XTide 2.9+) or zulu (previously)
          .xtide.xml: <xtideoptions z="n"/>

   [*] The National Ocean Service (NOS) defines both Mean Sea Level (MSL)
   and   Mean   Tide   Level  (MTL)  in  terms  of  averages  taken  over
   observations.   The  middle-level line is drawn at the midpoint of the
   theoretical tidal range, which usually corresponds to the mathematical
   mean  level  of  the predictions.  This approximates both MSL and MTL,
   but,   strictly   speaking,   is  equivalent  to  neither.   Moreover,
   subordinate  station  offsets  may shift the actual mean so that it no
   longer  falls  at  the midpoint of the tidal range.  The datum line is
   drawn  at the zero level of the predictions, which usually corresponds
   to the station's benchmark, but this too can be rendered inaccurate by
   subordinate station offsets.

Format of ~/.xtide.xml

   If  you  have compiled the interactive client (xtide), then you do not
   need  to  worry  about  ~/.xtide.xml at all, because the control panel
   will configure it for you automatically.

   In  the  event  that  you cannot use xtide but still need to make some
   settings  for  the  command  line client, use the example below as the
   starting point for your ~/.xtide.xml file.  This example just sets the
   TTY  geometry.   You  can  add more settings by adding more attributes
   (like  the  tw  and  th  attributes  shown  here)  to the xtideoptions
   entity.   The  attributes  that  are  recognized  for each setting are
   documented above.

<?xml version="1.0"?>
<xtideoptions tw="79" th="24"/>
     _________________________________________________________________

   [9]<- Previous [10]-> Next [11]Contents

References

   1. http://www.flaterco.com/xtide/xttpd.html
   2. http://www.flaterco.com/xtide/harmonics.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/advanced.html#cp
   6. http://www.flaterco.com/xtide/settings.html#splat
   7. http://www.flaterco.com/xtide/settings.html#splat
   8. http://www.flaterco.com/xtide/settings.html#splat
   9. http://www.flaterco.com/xtide/xttpd.html
  10. http://www.flaterco.com/xtide/harmonics.html
  11. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Portland Head Light

About harmonic constants and sub station corrections
(What to do if your location isn't listed)

   As  was explained in the [5]introduction, tide predictions for a given
   location  cannot  be  conjured  out  of the void--you need to get some
   special data for each and every location for which you want to predict
   tides.   XTide  reads these data from harmonics files.  Information on
   obtaining harmonics files is at
   [6]http://www.flaterco.com/xtide/files.html#harmonicsfiles.

   Currently  there  are  two  sources  of harmonics files.  David Flater
   maintains  a  conservative  set of data, emphasizing responsiveness to
   updates  and  traceability to authoritative sources instead of maximum
   coverage  of locations and historical predictions.  These data and the
   list    of    locations    they    support    can    be    found    at
   [7]http://www.flaterco.com/xtide/files.html#harmonicsfiles.        Bob
   Kenney  maintains a more liberal set of data, retaining some data that
   are old and expired in order to support users who continue to get good
   results  with  the  old  data.  These data and the much longer list of
   locations they support can be found at
   [8]http://harmonics.unh.edu/xtide/files.html.  Because they are out of
   date, use of these legacy data is not recommended.

   Check  to  make  sure  that  your location does not appear anywhere in
   these  harmonics  files by any alias.  If your location is not already
   on  the list, you need to obtain either a set of harmonic constants or
   a  set of corrections and send this information to David Flater and/or
   Bob  Kenney,  as  appropriate.   You  could import these data yourself
   using the tools available at
   [9]http://www.flaterco.com/xtide/files.html,  but  please  forward the
   data anyway so that others may benefit.

  Harmonic constants

   [10]National Ocean Service tide station at Bar Harbor, Maine

   Harmonic  constants  of  the  first  kind,  the kind worth having, are
   created by analysis of regular water level readings taken by automated
   tide  stations  like the one pictured here.  Harmonic constants of the
   second  kind,  the  kind not worth having, are created by mangling the
   first kind to approximate the results of applying corrections.  We are
   only interested in the first kind.  XTide can do corrections properly,
   so mangled data just junk up the database.

   [11]harmonics-dwf  contains  all  U.S. stations available from the NOS
   web  site.   If it has fallen out of date, email [12]dave@flaterco.com
   to check whether an update is in progress.

   In  countries  other  than the U.S., you might have a really hard time
   getting  the  resident  tide-predicting  authority to release harmonic
   constants.    They   may   be  paternalistic,  not  wanting  to  trust
   non-government  people with something as dangerous as tide prediction.
   They  may be fearful that the data will be used to time an invasion by
   sea.    Or  they  may  simply  want  to  retain  a  monopoly  on  tide
   predictions,  for  whatever  rea$on.   Regardless, if you do manage to
   obtain  harmonic constants, please obtain and forward a statement from
   the  authority  either  granting  permission for non-commercial use or
   explaining that such permission is not required.

   There  is  a collection of old harmonic constants for ports world wide
   that  had  to  be  withdrawn because of the permissions issue (for the
   full sob story, see the [13]FAQ).  If you have contact with your local
   marine  authorities  and could obtain and forward a statement that use
   of  these tide data is not restricted in your region, Mr. Kenney could
   reinstate the old data.  However, it would be better if they just sent
   us the newest data.

   If  you  have access to at least a year's worth of regular water level
   readings  for  some  locale,  you  can  derive  the harmonic constants
   yourself     using     the     Harmgen    program    available    from
   [14]http://www.flaterco.com/xtide/files.html#experts, or send the time
   series to [15]dave@flaterco.com (again, with all necessary permissions
   attached)  and  harmonic  constants  will  be  derived  for  you, time
   permitting.

  Corrections

   A subordinate station is a tide station whose predictions are obtained
   by applying corrections to a reference station, i.e., one for which we
   have good harmonic constants.  The words 'corrections,' 'differences,'
   and 'offsets' are used interchangeably.

   [16]harmonics-dwf  contains  all  U.S. stations available from the NOS
   web  site.   If it has fallen out of date, email [17]dave@flaterco.com
   to check whether an update is in progress.

   While harmonic constants can be hard to get, you should be able to get
   offsets  with  relative ease from a local boating magazine, chartbook,
   yacht  club,  or  marine authority.  If you find suitable offsets, you
   can  add  them to harmonics.tcd using the tideEditor program available
   from  [18]http://www.flaterco.com/xtide/files.html#extras.   There are
   two  other  ways  to  do  it  (via  build_tide_db  in tcd-utils or via
   Harmbase 2), but tideEditor is most expedient for the non-expert.

    General notes and warnings

     * There  are  many  different  flavors  of  offsets  for subordinate
       stations.   At  this  time,  XTide supports all commonly appearing
       flavors  except  for  the  Admiralty one that has different height
       differences  depending  on  the time of month.  The following rare
       and  freakish  sorts  are not supported:  those that use different
       offsets  depending  on  whether the flood at the reference station
       crossed some threshold; those that rely on more than one reference
       station;  those  that use different offsets for higher high or low
       water  versus lower high or low water; currents that use a regular
       tide station as reference, or vice-versa.
     * If  you  can't  find the latitude and longitude, just estimate the
       coordinates as best you can using an atlas.
     * The  timezone  attribute  is  only used to choose the time zone in
       which to render output for the location.  In the majority of cases
       this  will  be the same as for the reference station.  However, if
       your  reference  station is in a different time zone, you may need
       to alter the time offsets to REMOVE compensation for the time zone
       difference.  In XTide, offsets are independent of the time zone.
     * If  you  don't  get  slack  offsets (floodbegins, ebbbegins) for a
       current  station,  OMIT  those  fields!   When  slack  offsets are
       omitted,  XTide  will  interpolate a reasonable value.  But if you
       specify  zero,  you  get  zero--even  if  that's unreasonable with
       respect to the specified max and min.

    Adding corrections using tideEditor 1.4

   First make a backup copy of whatever you are about to modify.

   TideEditor  version  1.4  takes  the name of the file to modify as the
   command-line argument.

bash-3.1$ tideEditor whatever.tcd

   When  you  start tideEditor, you get a map of the world.  Point at the
   location where you want to add a subordinate station and right click.

   You  will  get  a  prompt  asking "Will the new station be a reference
   station or a subordinate station?"  Choose Subordinate.

   You  will  get  a  prompt  saying  "Please  select  the  new reference
   station."   Use the pull-down list to select the reference station and
   click OK.

   You  will  then  get  a  window  with  the  tabs General, Verbiage and
   Offsets, initially showing General.  On the General tab, the Reference
   Station,  Latitude  and  Longitude  fields will be pre-filled based on
   your  previous actions.  The other fields that you MUST fill in are as
   follows:
     * Station Name:  Enter the name of the new subordinate station.
     * Time  Zone:   Use  the  pull-down to set the time zone (select the
       major city for the applicable region).
     * Level Units:  Select feet or meters for tides, knots for currents.

   All  other  fields  on  the  General  and  Verbiage tabs are optional.
   Descriptions  of  the  other  fields are obtainable using the question
   mark tool thingy ( [whatsthis.png] ).

   The Offsets tab has the following fields.
     * Minimum Time Add.  The time adjustment for low tide / max ebb.  It
       is  expressed  as an integer that is hours times 100 plus minutes,
       so  for  -0:20 (negative 0 hours, 20 minutes) you would write -20,
       and  for  1:40  (positive 1 hour, 40 minutes) you would write 140.
       If you don't have this, leave it blank.
     * Minimum  Level  Add.   A  value,  in the units identified by Level
       Units,  that  is  added  to  the  tide  level  or current velocity
       predicted  at  low tide or max ebb.  If you don't have this, leave
       it blank.
     * Minimum  Level  Multiply.   A  multiplier  for  the  tide level or
       current  velocity  predicted at low tide or max ebb.  If you don't
       have this, leave it blank.
     * Maximum Time Add, Level Add, and Level Multiply are analogous, but
       correspond to high tide / max flood.
     * Flood Begins.  Another kind of "Time Add" used only by currents to
       adjust the time of the slack preceding a flood.  If you don't have
       this,  leave  it  blank.   If  it got initialized to zero, make it
       blank.
     * Ebb Begins.  Analogous to Flood Begins.

   When  finished,  click OK.  When you quit tideEditor, your new station
   will be saved in the updated TCD file.

   Notations used to describe corrections will vary:

    Notation              Translation
   -0:20       Time Add -20
   1 23        Time Add 123
   *1.07       Level Multiply 1.07
   +0.4        Level Add 0.4
   (*0.65+0.3) Level Multiply 0.65, Level Add 0.3

   If  you  were not given separate corrections for max and min, set both
   the max and min values to whatever you got.  For example, if you get

Head Harbor, Isle au Haut    -0:20   (Portland)

   then you should set both Minimum Tide Add and Maximum Time Add to -20.
     _________________________________________________________________

   [19]<- Previous [20]-> Next [21]Contents

References

   1. http://www.flaterco.com/xtide/settings.html
   2. http://www.flaterco.com/xtide/bugs.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/introduction.html
   6. http://www.flaterco.com/xtide/files.html#harmonicsfiles
   7. http://www.flaterco.com/xtide/files.html#harmonicsfiles
   8. http://harmonics.unh.edu/xtide/files.html
   9. http://www.flaterco.com/xtide/files.html
  10. http://www.flaterco.com/
  11. http://www.flaterco.com/xtide/files.html#harmonicsfiles
  12. mailto:dave@flaterco.com
  13. http://www.flaterco.com/xtide/faq.html#60
  14. http://www.flaterco.com/xtide/files.html#experts
  15. mailto:dave@flaterco.com
  16. http://www.flaterco.com/xtide/files.html#harmonicsfiles
  17. mailto:dave@flaterco.com
  18. http://www.flaterco.com/xtide/files.html#extras
  19. http://www.flaterco.com/xtide/settings.html
  20. http://www.flaterco.com/xtide/bugs.html
  21. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Lobster boat and the big ocean, Ogunquit, Maine, 1998-06-08.

Quirks to be aware of

    1. Graphs  actually begin a little bit earlier than the nominal start
       time  so  that  the specified start will appear immediately to the
       right  of  the labels for the depth axis instead of being obscured
       by them.
    2. The  effective  end  time for graph mode is entirely determined by
       the  start  time, the graph width, and the aspect.  If an end time
       is also specified by the user, it is ignored.
    3. XTide  uses shorter descriptions for the tide events listed across
       the  bottom  caption line in tide graphs whenever the descriptions
       get  to be longer than the timestamps.  Consequently, changing the
       time   format   setting  to  something  more  concise  causes  the
       descriptions to get shorter too, which is what you want.  However,
       this  behavior  can result in cosmetic inconsistencies; e.g., with
       default  settings,  "Mark  Rising" is matched by "Mark" instead of
       "Mark Falling," because the one additional letter puts it over.
    4. The  -o  command  line  switch causes output to be appended to the
       specified  file  instead  of  overwriting  it  as is the generally
       accepted custom.
    5. While  XTide-specific  command-line  arguments can be concatenated
       with their switches or not, the arguments to standard X11 switches
       sometimes  must  be  separate  to work.  Affected switches include
       -display, -fn, and -geometry.
    6. What  XTide  does  about  minimum  current  events  at subordinate
       stations  might  not  be  what  you expect.  See [5]Appendix B for
       details.

Known limitations

    1. RGB   color   specs  (rgb:N/N/N)  in  sizes  other  than  24  bits
       (rgb:hh/hh/hh) generally will not work.
    2. All timestamps have a precision of plus or minus one minute.
    3. All  predictions  are  made  to  an  accuracy of plus or minus one
       minute (in the mathematical sense, not in the sense of matching up
       with the real world).
    4. URLs  assigned  to  specific locations by the xttpd web server are
       rather  transient and will change whenever the harmonics files are
       updated.   The  xttpd web space will remain internally consistent,
       but hyperlinks from outside pages will be screwed.
    5. Moonrise and moonset don't work before 1900 or after 2099.
    6. The  time scale for stations claiming to be in UTC is not strictly
       speaking  UTC  since  it  does not implement [6]leap seconds.  The
       maximum  discrepancy  as  of  2007  is  23 seconds, which is still
       "below the noise."
    7. If  a  subordinate station has absurd offsets that cause low tides
       to become higher than high tides, the mathematical upper and lower
       bounds reported by stats mode may be incorrect.
    8. When  specifying location names on the command line, multiple data
       sets  having  the same name cannot be distinguished, and it is not
       deterministic which one you will get.
    9. XTide is untested and probably dysfunctional on any platform where
       time_t  is a non-integral type.  It would probably still work with
       --enable-time-workaround.

Known bugs

    1. If  the control panel is resized, dismissed, and then shown again,
       its  buttons are missing.  Cause of bug:  Don't know.  Workaround:
       Close  the control panel using the window manager (e.g., hit the ×
       in  the  upper  right corner) and then show it again.  The control
       panel retains its new size but the buttons reappear.
    2. Some  of  the  dialog  windows cause harmless but annoying toolkit
       warnings  when  you dismiss them.  Cause of bug:  Don't understand
       what the toolkit grabs are doing.  Workaround:  Ignore warnings.
    3. Line  width  in line graphs isn't maintained when the slope of the
       graph  becomes  drastic.  Cause of bug:  Need better algorithm for
       drawing line graphs.  Workaround:  Set the aspect higher.
    4. Buttons  will sometimes shift out from under the mouse pointer and
       get  "stuck  on."  Cause of bug:  (1) button moves due to changing
       geometry  of other things in the box, leading to (2) button shifts
       out  from  under  the  pointer,  which  triggers (3) bug in Athena
       Widgets where the button release event gets lost.  Workaround:  As
       needed,  click  on  the stuck button to un-stick it.  This problem
       can  be prevented in the control panel by specifying a fixed-width
       font  with  the  -fn  switch,  which  avoids (1).  The bug is less
       likely in other windows.
    5. The  analog  tide  clock icon flashes when it updates, and doesn't
       update  at  all  under  some  window managers.  Alternate symptom:
       Tide  clocks  crash  the  window manager at random.  Cause of bug:
       Window  managers  don't  expect  icons to keep changing and aren't
       designed to handle it properly.  Workaround:  Use a window manager
       that doesn't suck.
    6. Dialog  boxes  don't behave like you would expect when you hit the
       Enter  key.   Cause of bug:  Athena widgets use multi-line buffers
       even for one-line fields.  Workaround:  Don't hit Enter.
    7. Syslog  messages  generated  by  xttpd  have  timestamps in UTC or
       random  time zones intead of local time, which is highly confusing
       in  a  log that is otherwise in local time.  Cause of bug:  Design
       defect  of  syslog():  Every program logs in whatever time zone it
       happens to be using at the time instead of a standard zone.  XTide
       needs  to  adopt  the  time  zone  of  each  station  to  generate
       predictions for it.  Workaround:  none.
     _________________________________________________________________

   [7]<- Previous [8]-> Next [9]Contents

References

   1. http://www.flaterco.com/xtide/harmonics.html
   2. http://www.flaterco.com/xtide/faq.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/mincurrents.html
   6. http://www.boulder.nist.gov/timefreq/pubs/bulletin/leapsecond.htm
   7. http://www.flaterco.com/xtide/harmonics.html
   8. http://www.flaterco.com/xtide/faq.html
   9. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Perkins Cove, Maine, 1998-06-09

Frequently Asked Questions

   Note:   "Mumble Foo Bar" is a made-up place that is meant to represent
   whatever  place  you  are  looking  for.  Whatever is said in this FAQ
   about Mumble Foo Bar applies to your location as well.

  FAQ of the Day

     * [5]Are  these  predictions  compliant  with  the new 2007 Daylight
       Savings Time rules for the U.S.?

  Ultra-high frequency questions

     * [6]Your WWW Tide and Current Predictor blah blah blah...
     * [7]Can you send me predictions for Mumble Foo Bar?
     * [8]URGENT  -  DROP EVERYTHING AND READ THIS!  The race starts in 5
       hours so I need a tide chart for Mumble Foo Bar NOW!
     * [9]Can  you  tell  me where I can find a web page with predictions
       for Mumble Foo Bar?
     * [10]Can you please add predictions for Mumble Foo Bar?
     * [11]How do I make the calendar print all on one page?
     * [12]Can you tell me the offsets for Mumble Foo Bar?
     * [13]There  are multiple listings for the same place, and they give
       different results.  What's going on?
     * [14]Can  you  predict  the  tide  and/or current if I give you the
       latitude and longitude?
     * [15]The  coordinates  you  provide  for  Mumble Foo Bar are off by
       miles.
     * [16]Why are there no currents in the latest database?

  XTide operational questions

     * [17]I  am  doing some historical research and need to project what
       the tides would have been a long long time ago.
     * [18]I  live  outside  of  the  U.S.  and  my location is no longer
       supported.  What happened?
     * [19]The predictions for somewhere in the U.S.A., Mexico or Nunavut
       are off by one hour or six hours.
     * [20]For  Chesapeake  and Delaware Canal Current, Flood and Ebb are
       not informative.  Which way is which?
     * [21]For   Cape   Cod   Canal   Current,  Flood  and  Ebb  are  not
       informative.  Which way is which?
     * [22]When compiling XTide, I get errors like....
     * [23]I want to change the end time of a tide graph but the settings
       that I make have no effect.
     * [24]The text in XTide windows is formatted ugly.
     * [25]When  I run xttpd, it exits immediately with no errors to tell
       me what went wrong.
     * [26]I  always  get  a  warning  about  "using  obsolete  time zone
       database."
     * [27]How do I switch from tide to current predictions or vice-versa
       for a given location?
     * [28]What are bogo-knots?
     * [29]First  it  says high tide is at 3:15 PM but then when I run it
       again it says 3:14 PM.
     * [30]Has this been ported to Windows / PalmOS / anything but Unix?
     * [31]Xttpd sucks!  Can't XTide work with PHP?
     * [32]The tides for my location are totally wrong!
     * [33]The  tides for Mumble Foo Bar are obviously bogus because they
       have  too many high tides on this day / only one high tide on this
       day / tides that are just a few minutes apart.
     * [34]I  have five constituents and some seasonal corrections for my
       location.  Can you get this to work?

  General tide related questions

     * [35]I  have  a  tide  watch  that only goes through the year 1999.
       What year could I set it to that would be the same as this year?
     * [36]Is there a set time advancement each day for the next high and
       low tide?  Does it always repeat 12 1/2 hours later?
     * [37]Somebody  gave  me  a  tide clock, but the instructions say it
       only works on the east coast.  How can this be?
     * [38]Why  do  the  high and low tides have such different levels to
       them on any given day?
     * [39]If it's high tide here, is it low tide in [faraway place]?
     * [40]What does the zero (0) on a tide chart represent?
     * [41]Why  is  it  that  the  tides  two miles from here are an hour
       different than the tides here?
     * [42]Why  are  there  two  high tides per day, anyway?  How is this
       possible?
     * [43]What does "slack water" mean?
     * [44]I  have  a theory that [random phenomenon] is related to tidal
       forces,  but  I am landlocked.  Can you, like, predict the "tides"
       for [landlocked location]?
     * [45]I  want  to  write  my  own  tide predicting program.  Can you
       provide a SIMPLE explanation of the tide-predicting function?

  Business questions

     * [46]I  want  to  license XTide so I can build a commercial product
       around it.
     * [47]I  have  a  lot  of  specific  questions about the GNU General
       Public License and/or want a ruling that my specific plan is OK.
     * [48]We  are  a  non-profit  and  we  want  to  sell calendars with
       predictions from your web site.  Is that OK?
     * [49]I  have  a  great idea to make money selling tide predictions,
       but  I'm  not good with technical stuff, so would you just do this
       for me...
     * [50]I  already  make  money  selling tide prediction products, but
       your stuff is better, so would you just do this for me...
     * [51]I need to do [poorly researched brainstorm having something to
       do  with tide prediction]--how much would you charge in consulting
       fees to help me do it?

  Academic questions

     * [52]How should I cite XTide within publications?

  Questions that you should have asked, but didn't

     * [53]What  is  the  difference  between  a  reference station and a
       subordinate station?
     * [54]These predictions are nonsense--what is going on here?
     * [55]Where  can I find tons of information about tides that is both
       more authoritative and better written than this FAQ?
     _________________________________________________________________

  FAQ of the Day

   Q:  Are these predictions compliant with the new 2007 Daylight Savings
   Time rules for the U.S.?

   A:  XTide  relies  on  [56]the de facto standard time zone database to
   handle  Daylight  Savings  Time.   XTide's  results  will obey the new
   Daylight  Savings  Time  rules  if and only if the version of zoneinfo
   installed is sufficiently new.  See [57]System Requirements.

  Ultra-high frequency questions

   Q: Your WWW Tide and Current Predictor blah blah blah...

   A:  I am not the maintainer of the [58]WWW Tide and Current Predictor.
   I  am  the  maintainer  of  [59]XTide.   Although the [60]WWW Tide and
   Current  Predictor uses some version of [61]XTide behind the scenes, I
   have no control over the behavior of the web site or its maintenance.

   Q: Can you send me predictions for Mumble Foo Bar?

   A:  I  cannot  possibly  provide this level of service to everyone who
   wants it.  Please use a commercial service and/or a web site.

   Q: URGENT - DROP EVERYTHING AND READ THIS!  The race starts in 5 hours
   so I need a tide chart for Mumble Foo Bar NOW!

   A:  You  might  not  believe  it, but sometimes I go two weeks without
   reading  my  e-mail.  Really!  And when I do get back to it, there are
   always  lots  of messages just like this one, so far past their use-by
   dates  that green fuzz has started to grow on them.  The answer is the
   same:  I cannot possibly provide this level of service to everyone who
   wants it.  Please use a commercial service and/or a web site.

   Q:  Can  you  tell me where I can find a web page with predictions for
   Mumble Foo Bar?

   A:
     * Germany:  [62]Bundesamt für Seeschifffahrt und Hydrographie (BSH)
     * Netherlands:  [63]Ministerie van Verkeer en Waterstaat
     * New Zealand:  [64]Land Information New Zealand (LINZ)
     * Norway:  [65]Norwegian Hydrographic Service
     * U.K.:  [66]National Tidal and Sea Level Facility (NTSLF)
     * U.K.:  [67]U.K. Hydrographic Office
     * U.S.A.:   [68]National Ocean Service (NOS), Center for Operational
       Products and Services (CO-OPS)

   Q: Can you please add predictions for Mumble Foo Bar?

   A:  Probably  not.  Please read the section entitled [69]What to do if
   your location isn't listed.

   Q: How do I make the calendar print all on one page?

   A: The short answer for Windows XP users is to do the following:
    1. Bring the calendar up in Internet Explorer version 7 (not 6).
    2. Click  the  arrow to the right of the Print button, and then click
       Print Preview.
    3. Pull  down the print size menu ( Shrink To Fit ) and try different
       options until the calendar fits nicely on a page.
    4. When ready, click on the tiny printer icon to print.

   For a more complete answer and/or instructions tailored for Linux, see
   [70]Appendix C.

   Q: Can you tell me the offsets for Mumble Foo Bar?

   A:  You  can  get  them  easier  than  I  can  by checking the sources
   described  in  the  section  entitled  [71]What to do if your location
   isn't listed.

   Q:  There  are  multiple  listings  for  the same place, and they give
   different results.  What's going on?

   A:  There  are  two  different approaches to predicting the tides at a
   given  place.   One approach is to calculate them directly from a data
   set;  when this is done it is called a "reference station."  The other
   approach  is  to  estimate  them  using  adjustments to the tides at a
   nearby   reference   station;  when  this  is  done  it  is  called  a
   "subordinate station."

   Data  gathered  from  the  NOAA  web  site  sometimes  include  both a
   reference  station  and a subordinate station for the same place.  For
   example, the subordinate station may be used for published tide tables
   while the reference station is still relatively new and untested.  The
   results will differ, but they should be close (assuming that there are
   no  problems  with  the  data).   If  you are concerned about matching
   predictions  up with those from some particular source, you should try
   each data set and see which one matches the best.

   In  rare  cases,  data  gathered  from  the  NOAA web site include two
   reference  stations  or two subordinate stations with exactly the same
   name and nearly the same location.  When this happens, one of them has
   (2)  suffixed to its name.  Again, if you are trying to match official
   predictions, you should try both to determine which is better.

   If  you are using old legacy data or a web site that does, you may see
   additional  listings  for the same place.  These may be expired and/or
   have  dubious  traceability  to authoritative sources.  They cannot be
   expected to agree with up-to-date predictions.

   Q:  Can you predict the tide and/or current if I give you the latitude
   and longitude?

   A:  The  short  answer  is  no.  XTide cannot predict tides unless you
   provide  harmonic constants (see [72]What to do if your location isn't
   listed).

   From   what   I'm   told,   the  tide  models  that  were  built  from
   [73]TOPEX/Poseidon   data  work  on  a  global  scale,  but  they  are
   inaccurate   on   continental   shelves.    Some   organizations  have
   constructed  models  that  function  in  coastal  waters  in localized
   regions.   For example, NIWA has a [74]model for New Zealand's coastal
   waters,  and  NOAA  has  a [75]model of currents in San Francisco Bay.
   Although  XTide  could  make  use of harmonic constants generated from
   these models, XTide does not implement any such models.

   Q: The coordinates you provide for Mumble Foo Bar are off by miles.

   A:  XTide  reports  coordinates  in degrees only.  Some sources report
   coordinates  in  degrees  and  minutes  and  run  these  together in a
   confusing  way.   For  example,  a  coordinate  shown  as 2846.330 may
   actually  mean 28 degrees, 46.330 minutes, which XTide would report as
   28.7722 degrees.  If this is not sufficient to explain the discrepancy
   then  by  all means report the problem.  All coordinates in the latest
   harmonics data are traceable to an authoritative source.

   Q: Why are there no currents in the latest database?

   A:  The [76]Center for Operational Oceanographic Products and Services
   (CO-OPS)  of  [77]NOAA's  [78]National  Ocean  Service  (NOS) does not
   presently  supply  harmonic  constants  for currents on its public web
   site.   This  text from [79]http://tidesandcurrents.noaa.gov/ncop.html
   may partially explain why not:

     Approximately  70 percent of the stations in the 2001 Tidal Current
     Tables  are over 30 years old.  Many of these stations are based on
     analyses  of  less  than 7 days of data (the data duration is known
     for  24%  of  all  stations).   Channel dredging and changes in the
     configuration   of   ports   and   harbors   over  the  years  have
     significantly  altered  the  physical  oceanography  of many of the
     nation's estuaries.  Reports from local users indicate that many of
     NOS's  tidal current predictions may be inaccurate.  NOS intends to
     address these deficiencies by rebuilding the program and resampling
     the  currents  at  every  major port and estuary within the next 20
     years.

  XTide operational questions

   Q:  I  am  doing some historical research and need to project what the
   tides at Mumble Foo Bar would have been a long long time ago.

   A: This is generally ill-advised.

   It  is technically possible to get XTide to make projections back to 1
   AD  (see  [80]Appendix  A for details).  However, such projections are
   usually  unverifiable  and are likely to be wildly inaccurate.  If you
   work from these projections with no means of independent verification,
   you deserve what you get.

   The  perishability  of tide data for a given location varies depending
   on how quickly the local topography changes.  Some places go rotten in
   less  than  a  decade.  All locations are impacted by global sea level
   change, which becomes significant in less than a century.

   Over  even  longer  spans, the physics start to go wrong.  Some of the
   astronomical  "constants"  used  in the U.S. method of tide prediction
   really  aren't  constant;  they  change very slowly.  For example, the
   speeds  of  harmonic constituents change.  We are still using constant
   speeds  that  were  calibrated for the year 1900.  When you change the
   speeds of the harmonic constituents, it changes everything.  As we get
   too  far  away  from  1900  in  either direction, eventually the model
   collapses  and  the results are garbage.  As far as I know, nobody has
   done an analysis to determine exactly when this occurs.

   When  this  happens  in  the future, we can just update the speeds and
   generate fresh harmonic constants that work within the new model.  But
   we  can't do that for historical predictions because we don't have the
   water  level  observations  from  that period in history to derive the
   harmonic constants.  We have no choice but to use the physics of 1900,
   with  data  derived  from observations in 2000, to extrapolate back to
   whenever, and hope that we haven't pushed the model too far.

   Needless  to  say, the credibility of projections for anywhere reaches
   zero  well  before  you  get back to 1 AD.  So please don't ask for BC
   support.

   Q:  I live outside of the U.S. and my location is no longer supported.
   What happened?

   A:  After  a legal threat from the U.K. Hydrographic Office (UKHO) and
   the  subsequent  discovery that country-by-country permissions are now
   required to use harmonic constants (the data needed to predict tides),
   all of the data that arrived via the International Hydrographic Office
   (IHO)  or  the Table des Marées des Grands Ports du Monde (TMGPM) were
   removed from the harmonics files in January 2001.

   Back  in  the  old  days, the collection of hydrographic data was done
   almost   exclusively  using  public  funds.   The  resulting  harmonic
   constants   were   treated   as  scientific  results,  published,  and
   distributed  on  request  from an international data bank.  But in the
   late  20th  century,  a  wave of privatizations occurred, and harmonic
   constants became the intellectual property of the collecting agencies.

   You  wouldn't  think  it  possible  to  "un-publish"  data  that  were
   distributed  with considerable freedom at one time.  Nevertheless, the
   international data bank was abolished, the Table des Marées des Grands
   Ports  du Monde was withdrawn from publication, and I was coerced into
   removing the associated data from the harmonics files.

   Was  I  spineless?   Perhaps.   Those who wrote the threatening letter
   clearly  had  not  done  their homework and may have overreached their
   jurisdiction.   But even with the benefit of hindsight and experience,
   knowing that some unethical companies habitually make legal threats to
   manipulate  people  into  doing  things  that  they aren't necessarily
   obliged  to  do, I don't blame myself for not fighting it.  Why take a
   risk for the sake of some tide data of questionable pedigree that were
   doomed to become useless from age pretty soon anyway?

   For  my  own  part,  I  do not consider privatization to be inherently
   evil.   It  would  have  been  reasonable to keep newly generated data
   secret  while  leaving  the  old data in the public domain until their
   useful  life  expired.  But in my opinion it was wrong to lay claim to
   the  old  data  that  were  once  shared  in  the spirit of scientific
   openness.   It was a disservice and dishonor to all of us who accepted
   those data on good faith and donated our own time to maintain them and
   add  value  to  them to end up accused of copyright infringement.  For
   someone  who had invested himself in writing free software as a public
   service, the reward was a slap in the face.

   Although  only  the  UKHO  made an issue of it, the fact that they did
   sufficed  to "poison" all of the IHO and TMGPM data for every country.
   We  can  no  longer assume that we have permission to use any of them.
   In  countries other than the U.K., if you have contact with your local
   marine  authorities  and  could  obtain  and  forward  to Mr. Kenney a
   statement  that  use of the old data is not restricted in your region,
   they could be reinstated.  (Bob Kenney is the maintainer of a database
   of  legacy data that can be used by XTide and other programs.  You can
   find it on his web site at
   [81]http://harmonics.unh.edu/xtide/files.html.)  However, if they have
   newer  data,  it would be better if they just sent those to me and Mr.
   Kenney  with all necessary permissions attached.  I regret that former
   British colonies having no independent tide authority have effectively
   been disenfranchised.

   In  2003-12,  new  data  for  44 stations in the U.K. became available
   thanks  to the generosity of the [82]British Oceanographic Data Centre
   (BODC)   based   at   the  [83]Proudman  Oceanographic  Laboratory  in
   Liverpool.      The     legal     details     can    be    found    at
   [84]http://flaterco.com/pol.html.  I encourage other organizations who
   maintain  tide  gauges  anywhere  in  the  world  to  contact us about
   deriving some harmonic constants.

   Q:  The predictions for somewhere in the U.S.A., Mexico or Nunavut are
   off by one hour or six hours.

   A:  The  referenced  nations  have recently made changes to their time
   zones  or  daylight  savings  time  rules.  In order for XTide to give
   predictions  in local time correctly, a recent version of the Zoneinfo
   library   must  be  installed.   You  can  obtain  this  library  from
   [85]ftp://elsie.nci.nih.gov/pub/.

   Q:  For  Chesapeake  and Delaware Canal Current, Flood and Ebb are not
   informative.  Which way is which?

   A:  Based  on  observations  by  Richard  W.  Reynolds and friends, it
   appears that "Flood" for this data set indicates that water is flowing
   from the Chesapeake to the Delaware bay.

   Q:  For  Cape  Cod  Canal  Current, Flood and Ebb are not informative.
   Which way is which?

   A:  According  to  Reinhard  Schumann, "Flood" for this data set means
   "current towards the east."  Woods Hole current is probably the same.

   Q: When compiling XTide, I get errors like....

   A: Please refer to the [86]troubleshooting section of the installation
   instructions.   If  your  error  is  not  shown  there,  please  email
   [87]dave@flaterco.com for assistance.

   Q: I want to change the end time of a tide graph but the settings that
   I make have no effect.

   A: This is [88]Quirk #2.  In graph mode, the end time is determined by
   the  applicable  width  and  aspect,  not the other way around.  Thus,
   neither  the -e switch nor the compiled-in defpredictinterval constant
   have  any  effect  in  this  case.  In the interactive client, you can
   resize  the  window as you would any window and change the aspect from
   the  Options  menu.   The applicable command-line switches are -gw for
   X-windows  or  PNG  formats,  -tw  for text format, and -ga.  For more
   details, refer to "[89]Customizing XTide."

   Q: The text in XTide windows is formatted ugly.

   A:  For  windows  containing lots of text, XTide uses the default font
   offered  by the X11 environment.  If this is not a monospace font, the
   results  could  indeed  be  ugly.   The default font can be overridden
   using the command line switch -fn.  Give this a try:

     xtide -fn "-adobe-courier-bold-r-normal-*-12-*-*-*-*-*-iso8859-1"

   If that looks better, you can make the change permanent by adding this
   line to your ~/.Xresources file:

     XTide*font: -adobe-courier-bold-r-normal-*-12-*-*-*-*-*-iso8859-1

   Q:  When  I  run xttpd, it exits immediately with no errors to tell me
   what went wrong.

   A: When executed, xttpd immediately dissociates from your terminal and
   starts  logging  all  diagnostics  to  syslog.  So look in your system
   logs.  You will find these someplace like /var/log or /var/adm/log.

   Q: I always get a warning about "using obsolete time zone database."

   A:  Please see the [90]System requirements section for details of what
   this means and what you can do to fix it.

   Q:  How do I switch from tide to current predictions or vice-versa for
   a given location?

   A: Alas, although the two are clearly connected in the physical world,
   they  are  unrelated from the perspective of XTide.  Even for the same
   location,   tide  predictions  and  current  predictions  require  two
   completely  separate  data  sets, and rarely will you get both.  As of
   2005-01,  there  are  no  currents  available  in the latest data (the
   National  Ocean  Service  has  not  made  them  available on their web
   site).   If current predictions are available for a location in legacy
   data, they will appear in the location list with the word "Current" at
   the end of the name.

   Q: What are bogo-knots?

   A:  If  you are still seeing bogo-knots, then you are definitely using
   obsolete  data  and  an  obsolete version of XTide, or accessing a web
   site  that is using obsolete data and an obsolete version of XTide.  I
   am not the maintainer of any such web sites, and I recommend upgrading
   to  XTide  2,  which will barf all over any harmonics files that still
   contain "bogo-knots."

   Q:  First it says high tide is at 3:15 PM but then when I run it again
   it says 3:14 PM.

   A:  XTide's  accuracy  is plus or minus one minute.  The behavior that
   you witnessed is normal.

   Q: Has this been ported to Windows / PalmOS / anything but Unix?

   A: Yes, to varying degrees.  Please see the [91]ports page.

   Q: Xttpd sucks!  Can't XTide work with PHP?

   A: A number of people have expressed interest in getting XTide to work
   through PHP.  Thus far I have just been introducing them to each other
   through  e-mail and waiting for cool things to happen.  There is now a
   [92]WordPress plugin by Mir Rodríguez.

   Q: The tides for my location are totally wrong!

   A:  Unfortunately,  there  have  been some problems recently with data
   sets being assigned the wrong meridians upstream.  The symptom is that
   all  predictions  are  shifted  earlier or later by the same number of
   hours.   If  you  can verify that this has happened by comparison with
   published tide tables (available at
   [93]http://tidesandcurrents.noaa.gov/tides07/),   please   report  the
   problem for corrective action.

   Q:  The tides for Mumble Foo Bar are obviously bogus because they have
   too  many  high  tides  on this day / only one high tide on this day /
   tides that are just a few minutes apart.

   A: That is not necessarily a problem.  Some places really do have only
   one  tide cycle per day.  Others generate "extra" tides when the tidal
   forces  align  in such a way as to produce a "double" high or low tide
   or  a  temporary  reversal  near  mid-tide.   These extra tides can be
   arbitrarily close together.  Official predictions might omit them, but
   XTide faithfully reports all maxima and minima that it finds.

   The  legacy  data  contain  some data sets in which harmonic constants
   were  generated for subordinate stations by munging the constants of a
   reference station.  This operation was fragile and sometimes it led to
   spurious maxima and minima.  The fix is to upgrade to the latest data,
   which contains no "munged" data sets.

   Q:  I  have  five  constituents  and  some seasonal corrections for my
   location.  Can you get this to work?

   A:  XTide  is  not  presently  enabled  to handle seasonal corrections
   directly.   To  my  knowledge,  seasonal  corrections are only used in
   publications by the British Admiralty that do not allow redistribution
   of  data,  so  the value of providing better support for them in XTide
   would  be marginal at best.  However, if you have legal access to such
   data  and  are  determined to use it with XTide, it may be possible to
   synthesize  values  for  long-term  constituents  to  "approximate the
   approximation."   A  spreadsheet  for  doing  this  is  available from
   [94]http://www.flaterco.com/xtide/files.html#experts.

   It might also help to enable constituent inference in XTide.  This can
   be done from the [95]control panel or using the [96]infer setting.

  General tide related questions

   Q:  I  have  a  tide watch that only goes through the year 1999.  What
   year could I set it to that would be the same as this year?

   A: Sorry.  It just doesn't work like that.

   Q:  Is there a set time advancement each day for the next high and low
   tide?  Does it always repeat 12 1/2 hours later?

   A:  No.   The  12 hour 25 minute cycle is literally only a first-order
   approximation.   Most tide predictions involve twenty to thirty terms,
   and  some  require  over  a hundred.  The 12:25 cycle is just the most
   dominant term.

   Q:  Somebody  gave  me  a tide clock, but the instructions say it only
   works on the east coast.  How can this be?

   A:  "Dumb"  tide  clocks  assume  that  the  12  hour  25 minute cycle
   mentioned   in   the   [97]previous   question   is   a   good  enough
   approximation.   For  the  west  coast,  it isn't.  The following tide
   graphs  illustrate  the differences between east and west coast tides.
   The  high  and low tide times that would be indicated by a "dumb" tide
   clock  are  shown  with  vertical yellow lines.  San Francisco shows a
   2-hour discrepancy on the lower high tide.

   Emulation of dumb tide clock for Bangor, Maine

   Emulation of dumb tide clock for San Francisco, California

   Q: Why do the high and low tides have such different levels to them on
   any  given  day?   Does  it  actually coincide with the amount of pull
   exerted by the phase or closeness of the moon?

   A:  The  tides  do  not coincide too closely with the moon.  While the
   moon  produces  most  of  the  force  that drives them, the exact tide
   levels  result  from the sloshing around of huge amounts of water, the
   effects of the shape of the coastline, and things like that.

   Q: If it's high tide here, is it low tide in [faraway place]?

   A:  It's  hard  to infer anything over large distances since localized
   effects can have a huge influence on tides.

   Q: What does the zero (0) on a tide chart represent?

   A:  Tide heights are given relative to the "datum" which in most cases
   is  one  of  several  benchmarks corresponding to low tides of varying
   extremeness.   The  preferred  benchmark in the U.S. is Mean Lower Low
   Water  (MLLW).   The  odds of the predicted tide getting below MLLW on
   any  given  day  are  about  half.   The  preferred  benchmark  in the
   Netherlands  is  Mean  Low  Water  Springs (MLWS).  MLWS is lower than
   MLLW.   The  predicted  tide will get below MLWS on average only about
   twice   a  month.   The  preferred  benchmark  in  Germany  is  Lowest
   Astronomical  Tide  (LAT).  LAT is the lowest tide predicted over a 19
   year  period.   The  predicted  tide will not get below LAT in that 19
   year period, and is unlikely to get below it by any significant amount
   ever.

   In  harmonics-dwf,  some U.S. locations for which a MLLW benchmark was
   unavailable  use  an  estimated value of MLLW that is derived from the
   predictions.   These  estimates  tend to yield predictions that differ
   from  National  Ocean Service published tables by (0.1-0.2) ft.  Older
   versions of harmonics-dwf used LAT for these stations, which of course
   yielded much larger discrepancies.

   For  more  information  on  datums,  read  the  National Ocean Service
   publication [98]Tidal Datums and their Applications.

   Q:  Why is it that the tides two miles from here are an hour different
   than  the  tides  here?   If the tidal bulge follows the moon at 1,000
   miles per hour, how can the difference be so great?

   A:  When  the water tries to follow the moon, it runs up against a lot
   of  obstacles,  including its own inertia, the shape of the coastline,
   and  the resonances that are set up by the continual tidal motion.  In
   some  cases the tides are fighting a permanent current, e.g., going up
   a  river, and this slows down the tidal crest.  The result is that the
   tides  at any one place at any given time don't have a whole lot to do
   with the moon any more.

   Q:  Why  are  there  two  high  tides  per  day,  anyway?  How is this
   possible?

   A:  The  standard  simple answer to this question is that the water on
   the  side  of  the earth opposite the moon bulges out due to decreased
   lunar  gravity in the same way that the water on the side of the earth
   nearest  the  moon bulges out due to increased lunar gravity.  This is
   counter-intuitive  in  that  one might expect all of the water to just
   rush  over  to  the  side where the moon is.  To explain this, I quote
   from     "Our     Restless     Tides,"     a    NOAA    tutorial    at
   [99]http://tidesandcurrents.noaa.gov/restles1.html:

     To all outward appearances, the moon revolves around the earth, but
     in  actuality,  the  moon  and  earth revolve together around their
     common center of mass, or gravity.  The two astronomical bodies are
     held  together  by gravitational attraction, but are simultaneously
     kept  apart  by an equal and opposite centrifugal force produced by
     their  individual  revolutions  around  the  center-of-mass  of the
     earth-moon  system.   This  balance of forces in orbital revolution
     applies  to  the  center-of-mass of the individual bodies only.  At
     the  earth's surface, an imbalance between these two forces results
     in  the  fact  that  there  exists,  on the hemisphere of the earth
     turned  toward  the  moon,  a  net (or differential) tide-producing
     force  which  acts  in  the  direction  of the moon's gravitational
     attraction,  or  toward the center of the moon.  On the side of the
     earth  directly  opposite the moon, the net tide-producing force is
     in the direction of the greater centrifugal force, or away from the
     moon.

   Q: What does "slack water" mean?

   A:  This  and  many  other  terms  are  defined  in the [100]NOAA tide
   glossary.

   Q:  I  have  a  theory  that  [random  phenomenon] is related to tidal
   forces,  but  I am landlocked.  Can you, like, predict the "tides" for
   [landlocked location]?

   A:  There  is  no support for this in XTide (ocean tides have only the
   vaguest  connection  to  latitude,  longitude, and the position of the
   moon),  but you can find relevant information by searching the web for
   "land tide."

   Q:  I want to write my own tide predicting program.  Can you provide a
   SIMPLE explanation of the tide-predicting function?

   A:  The  tide  prediction  function is fairly simple, requiring only a
   cosine  function.   The  piles  of code surrounding it in XTide are to
   optimize  the  process of finding maxima and minima.  This can be done
   less  optimally  with  significantly  less  code  and effort (as early
   versions of XTide did).

   Since  it  is  hard  to  draw  summation symbols in ASCII, here is the
   pseudocode instead:

Height = Datum;
for a = 1 to numconst
  Height = Height +
    amplitude[a] * nodefactor[a] * cos (speed[a] * time + phase[a])
next a

   The  datum is provided at the top of the data set in the harmonics.txt
   file.

   The  amplitudes are the first column of numbers in the data set in the
   harmonics file.

   The  node  factors  are  tabulated  for  each  year  at the top of the
   harmonics  file,  or  can be calculated from scratch using the code in
   the Congen program, available in
   [101]http://www.flaterco.com/xtide/files.html#experts.    Most  likely
   you will just want to tabulate them.

   The  speeds  of the numconst constituents are listed at the top of the
   harmonics file in degrees per hour.

   If  speed  is in degrees or radians per X, then time is in X since the
   beginning  of  the  year.  The specific time zone for the beginning of
   the year is chosen as described below.

   Phase  includes  a  yearly  adjustment called the equilibrium argument
   that is tabulated at the top of the harmonics file (or calculated from
   scratch  like  the  node  factors), minus the location-specific phases
   that  are  the  second  column  of  numbers  in the data set (given in
   degrees).   By  default,  you  will  get  phases such that the time is
   measured  from  January  1  00:00  in  the  time zone specified by the
   meridian.  Customarily, the meridian is chosen to be the standard time
   of  the  location  in  question  to  make  life  easier on simple tide
   prediction  programs  that  don't  mess with time zones or summer time
   adjustments.  In the harmonics.txt file, you will find the meridian of
   each  data  set  right  before  the time zone identifier, in hours and
   minutes:  e.g., -05:00 :America/Montreal.  It is trivial to adjust the
   phases  of the constituents for any desired meridian.  What XTide does
   is adjust them all to UTC and then use the Unix time zone functions to
   render the output with Daylight Savings Time and everything.

  Business questions

   Q:  I want to license XTide so I can build a commercial product around
   it.

   A:  XTide  is  released  under  the  terms  of  the GNU General Public
   License.  [102]This FAQ about the GPL may be applicable to you.

   XTide  has  been used by commercial packages "at arm's length," to use
   the  wording  of  the FAQ cited above, but I have never licensed it by
   any  terms  other  than  the  GPL, nor have I ever offered any kind of
   warranty  or  service  that  one  might  expect  if  it  were licensed
   commercially.

   PLEASE  NOTE:   The  question  whether you can use XTide is completely
   separate  from  the  question  of  whether  you  can use the tide data
   (harmonics files).  In general, data for U.S. ports are public domain,
   while   others   are  for  non-commercial  use  only.   [103]Read  the
   boilerplate for details.

   Q:  I  have  a  lot of specific questions about the GNU General Public
   License and/or want a ruling that my specific plan is OK.

   A: Please read the GPL FAQ, available [104]here or [105]here.  If that
   does   not   answer   your   question,   the  people  to  ask  are  at
   [106]licensing@fsf.org.

   Q:  We are a not-for-profit organization and we want to sell calendars
   with predictions from your web site.  Is that OK?

   A: Firstly, it's not my web site.  See [107]Question 1.  Secondly, all
   predictions  for  places  outside  the U.S. are for non-commercial use
   only  (i.e.  you  can't  sell them no matter what your tax status is).
   Lastly,  if  you  do want to sell calendars containing predictions for
   the U.S., you must include all of the "NOT FOR NAVIGATION" disclaimers
   and agree to accept full liability in case someone has a problem.

   Legalities  aside,  my  opinion  has  always  been that people who are
   selling tide predictions have no business selling anything that is not
   directly  certified by the [108]National Ocean Service.  Beggars can't
   be  choosers,  but  when  people are paying for something, they have a
   right to hold you to a higher standard.

   Q: I have a great idea to make money selling tide predictions, but I'm
   not good with technical stuff, so would you just do this for me...

   A: No.

   Q:  I  already  make  money selling tide prediction products, but your
   stuff is better, so would you just do this for me...

   A: No.

   Q:  I  need to do [poorly researched brainstorm having something to do
   with tide prediction]--how much would you charge in consulting fees to
   help me do it?

   A:  It's  moot.  Your plan won't work for one or more of the following
   reasons:
     * You  think  that  it's  possible  to  predict  tides for arbitrary
       locations based on just the latitude and longitude.  It's not.
     * You  are  assuming  that  a  database  of quality-assured harmonic
       constants  for  ports  worldwide  is  obtainable.   It isn't.  See
       [109]news about data maintenance and the [110]outside-the-U.S. FAQ
       for background.
     * The harmonic constants that you plan to use are encumbered in ways
       that make what you want to do with them illegal.
     * You  think that harmonic constants can be burned into the firmware
       of  an embedded device and never need maintenance.  They can't be;
       they need to be updated regularly.
     * You  think  that  you can cut corners with a simple tide clock and
       still  get  tide  predictions  that match those published by NOAA.
       You can't.

  Academic questions

   Q: How should I cite XTide within publications?

   A:  The  web  site  is  the  best  thing  you can cite.  For a general
   reference to XTide, I suggest the following, with the current date.

     [1]    David   Flater.    XTide.    http://www.flaterco.com/xtide/.
     2005-07-04.

   If  you  are  using  specific  predictions from XTide rather than just
   XTide  in  general, then you should cite the specific version of XTide
   and  the  specific data file that you used.  In this case, it would be
   appropriate  to  use  the  date  indicated  in  the changelog for that
   version of XTide and the revision date of the data file.

     [2]  David Flater.  XTide version 2.8.2.
     http://www.flaterco.com/xtide/.  2005-01-06.

     [3]        harmonics-dwf-2005-06-05-v2.        Available       from
     http://www.flaterco.com/xtide/files.html, 2005-06-05.

  Questions that you should have asked, but didn't

   Q:   What  is  the  difference  between  a  reference  station  and  a
   subordinate station?

   A:  The  following information was copied from [111]NOAA's web site on
   2007-02-17.

     The  publication  of  full  daily  tide  predictions is necessarily
     limited  to  a  comparatively  small  number  of  stations.   These
     stations are referred to as "reference stations".  Tide predictions
     for  more  than  3000  other locations, referred to as "subordinate
     stations",  can be obtained by applying specific differences to the
     daily tide predictions for one of the reference stations.  [...]

     Caution:   The time differences and height ratios used to calculate
     predictions  at  subordinate stations are derived from a comparison
     of  simultaneous  tide  observations at the subordinate station and
     its  reference  station.   Because  these adjustments are constant,
     they  may not always provide for the daily variations in the actual
     tides,  especially if the subordinate station is some distance from
     the reference station.  Therefore, although the application of time
     differences  and  height  ratios  will generally provide reasonably
     accurate  approximations,  they  cannot  result  in  predictions as
     accurate  as  those  listed  for  the reference stations, which are
     based on much larger periods of analysis.

   In  plain  language,  what  you need to know is this:  All subordinate
   station  predicions  are  approximate.  Tide predictions are always at
   best approximations of reality, but for subordinate stations that goes
   double.

   Q: These predictions are nonsense--what is going on here?

   Tide graph with a weird zigzag
2007-02-14 12:57 PM AKST   3.46 feet  High Tide
2007-02-14  3:00 PM AKST   Moonset
2007-02-14  7:08 PM AKST   Sunset
2007-02-14  9:06 PM AKST  -0.38 feet  Low Tide
2007-02-15  6:46 AM AKST   3.08 feet  Low Tide
2007-02-15  7:00 AM AKST   2.62 feet  High Tide
2007-02-15  9:07 AM AKST   Moonrise
2007-02-15  9:22 AM AKST   Sunrise
2007-02-15  1:46 PM AKST   3.46 feet  High Tide

   Current graph with weird double-flood
2004-03-31  5:01 AM PST  -0.64 knots  Max Ebb
2004-03-31  5:49 AM PST   Sunrise
2004-03-31 10:06 AM PST   0.02 knots  Max Flood
2004-03-31 10:18 AM PST   0.00 knots  Slack, Flood Begins
2004-03-31 11:21 AM PST  -0.00 knots  Slack, Ebb Begins
2004-03-31  1:01 PM PST   Moonrise
2004-03-31  4:13 PM PST  -0.90 knots  Max Ebb

   These   are  extreme  examples  of  what  can  happen  when  the  time
   differences  and height ratios for subordinate stations don't "provide
   for  the  daily  variations  in  the  actual  tides."  Although in the
   average  case  the  offsets might yield good results, in extreme cases
   they  can  yield  nonsense  results  like  tide events happening in an
   impossible order or a "low" tide actually being higher than the "high"
   tide  right  next to it.  There is nothing XTide can do to rationalize
   these  paradoxes,  and  the  tide levels that are interpolated between
   paradoxical events are essentially garbage.

   Q:  Where can I find tons of information about tides that is both more
   authoritative and better written than this FAQ?

   A: [112]http://tidesandcurrents.noaa.gov/education.html
     _________________________________________________________________

   [113]<- Previous [114]-> Next [115]Contents

References

   1. http://www.flaterco.com/xtide/bugs.html
   2. http://www.flaterco.com/xtide/design.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/faq.html#DST
   6. http://www.flaterco.com/xtide/faq.html#5
   7. http://www.flaterco.com/xtide/faq.html#40
   8. http://www.flaterco.com/xtide/faq.html#45
   9. http://www.flaterco.com/xtide/faq.html#20
  10. http://www.flaterco.com/xtide/faq.html#10
  11. http://www.flaterco.com/xtide/faq.html#onepage
  12. http://www.flaterco.com/xtide/faq.html#50
  13. http://www.flaterco.com/xtide/faq.html#duplicates
  14. http://www.flaterco.com/xtide/faq.html#51
  15. http://www.flaterco.com/xtide/faq.html#100
  16. http://www.flaterco.com/xtide/faq.html#nocurrents
  17. http://www.flaterco.com/xtide/faq.html#HistoricalPredictions
  18. http://www.flaterco.com/xtide/faq.html#60
  19. http://www.flaterco.com/xtide/faq.html#65
  20. http://www.flaterco.com/xtide/faq.html#70
  21. http://www.flaterco.com/xtide/faq.html#80
  22. http://www.flaterco.com/xtide/faq.html#90
  23. http://www.flaterco.com/xtide/faq.html#92
  24. http://www.flaterco.com/xtide/faq.html#93
  25. http://www.flaterco.com/xtide/faq.html#95
  26. http://www.flaterco.com/xtide/faq.html#100
  27. http://www.flaterco.com/xtide/faq.html#110
  28. http://www.flaterco.com/xtide/faq.html#130
  29. http://www.flaterco.com/xtide/faq.html#140
  30. http://www.flaterco.com/xtide/faq.html#150
  31. http://www.flaterco.com/xtide/faq.html#php
  32. http://www.flaterco.com/xtide/faq.html#210
  33. http://www.flaterco.com/xtide/faq.html#220
  34. http://www.flaterco.com/xtide/faq.html#250
  35. http://www.flaterco.com/xtide/faq.html#52
  36. http://www.flaterco.com/xtide/faq.html#170
  37. http://www.flaterco.com/xtide/faq.html#DumbTideClock
  38. http://www.flaterco.com/xtide/faq.html#160
  39. http://www.flaterco.com/xtide/faq.html#180
  40. http://www.flaterco.com/xtide/faq.html#190
  41. http://www.flaterco.com/xtide/faq.html#200
  42. http://www.flaterco.com/xtide/faq.html#230
  43. http://www.flaterco.com/xtide/faq.html#240
  44. http://www.flaterco.com/xtide/faq.html#255
  45. http://www.flaterco.com/xtide/faq.html#260
  46. http://www.flaterco.com/xtide/faq.html#55
  47. http://www.flaterco.com/xtide/faq.html#56
  48. http://www.flaterco.com/xtide/faq.html#calendar
  49. http://www.flaterco.com/xtide/faq.html#54
  50. http://www.flaterco.com/xtide/faq.html#300
  51. http://www.flaterco.com/xtide/faq.html#667
  52. http://www.flaterco.com/xtide/faq.html#cite
  53. http://www.flaterco.com/xtide/faq.html#refsub
  54. http://www.flaterco.com/xtide/faq.html#timewarp
  55. http://www.flaterco.com/xtide/faq.html#NOAA_education
  56. ftp://elsie.nci.nih.gov/pub/
  57. http://www.flaterco.com/xtide/sysreq.html#TZsysreq
  58. http://tbone.biol.sc.edu/tide/sitesel.html
  59. http://www.flaterco.com/xtide/
  60. http://tbone.biol.sc.edu/tide/sitesel.html
  61. http://www.flaterco.com/xtide/
  62. http://www.bsh.de/en/Marine%20data/Forecasts/Tides/index.jsp
  63. http://www.getij.nl/engels/
  64. http://www.hydro.linz.govt.nz/tides/majports/index.asp
  65. http://vannstand.statkart.no/Engelsk/skjema.php
  66. http://www.pol.ac.uk/ntslf/tides/
  67. http://easytide.ukho.gov.uk/
  68. http://tidesandcurrents.noaa.gov/tide_pred.html
  69. http://www.flaterco.com/xtide/harmonics.html
  70. http://www.flaterco.com/xtide/pound_to_fit.html
  71. http://www.flaterco.com/xtide/harmonics.html
  72. http://www.flaterco.com/xtide/harmonics.html
  73. http://topex-www.jpl.nasa.gov/mission/topex.html
  74. http://www.niwa.co.nz/services/tides
  75. http://sfports.wr.usgs.gov/SFPORTS/vec_map/vec_map.html
  76. http://tidesandcurrents.noaa.gov/
  77. http://www.noaa.gov/
  78. http://oceanservice.noaa.gov/
  79. http://tidesandcurrents.noaa.gov/ncop.html
  80. http://www.flaterco.com/xtide/time_t.html
  81. http://harmonics.unh.edu/xtide/files.html
  82. http://www.bodc.ac.uk/
  83. http://www.pol.ac.uk/
  84. http://flaterco.com/pol.html
  85. ftp://elsie.nci.nih.gov/pub/
  86. http://www.flaterco.com/xtide/installation.html#trouble
  87. mailto:dave@flaterco.com
  88. http://www.flaterco.com/xtide/bugs.html
  89. http://www.flaterco.com/xtide/settings.html
  90. http://www.flaterco.com/xtide/sysreq.html
  91. http://www.flaterco.com/xtide/ports.html
  92. http://www.almanaqueazul.org/?p=132
  93. http://tidesandcurrents.noaa.gov/tides07/
  94. http://www.flaterco.com/xtide/files.html#experts
  95. http://www.flaterco.com/xtide/advanced.html#cp
  96. http://www.flaterco.com/xtide/settings.html#infer
  97. http://www.flaterco.com/xtide/faq.html#170
  98. ftp://ftp.flaterco.com/xtide/tidal_datums_and_their_applications.pdf
  99. http://tidesandcurrents.noaa.gov/restles1.html
 100. ftp://ftp.flaterco.com/xtide/glossary2.pdf
 101. http://www.flaterco.com/xtide/files.html#experts
 102. http://www.gnu.org/licenses/gpl-faq.html#GPLInProprietarySystem
 103. http://www.flaterco.com/xtide/harmonics_boilerplate.txt
 104. http://www.fsf.org/licensing/licenses/gpl-faq.html
 105. http://www.gnu.org/licenses/gpl-faq.html
 106. mailto:licensing@fsf.org
 107. http://www.flaterco.com/xtide/faq.html#5
 108. http://oceanservice.noaa.gov/
 109. http://www.flaterco.com/xtide/news.html#datamaint
 110. http://www.flaterco.com/xtide/faq.html#60
 111. http://tidesandcurrents.noaa.gov/t2help.html
 112. http://tidesandcurrents.noaa.gov/education.html
 113. http://www.flaterco.com/xtide/bugs.html
 114. http://www.flaterco.com/xtide/design.html
 115. http://www.flaterco.com/xtide/xtide.html#contents

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   [4]Sunset over the bar, Bar Harbor, Maine, 1997-06-24

Design notes

  Principles

     * Portability
          + The  scope  is  all "reasonably modern" flavors of Unix, X11,
            and C++
          + Limit language features to those that reliably compile
          + Respect the holy mantra "./configure; make; make install"
          + Allow     trivial     workarounds     for    platform-    and
            distribution-specific bugs or special requirements
          + Disallow  nontrivial workarounds and those that conflict with
            correct operation on non-broken platforms
     * Availability
          + Limit  dependencies  on external tools and libraries to those
            that are typically pre-installed
     * Usability
          + Maximize orthogonality of settings and switches
          + Support both interactive and non-interactive use
          + Command-line  switches  should be no more than two characters
            long
     * Maintainability
          + Accept no bogus patches
          + Maximize orthogonality of modules
     * Stability
          + Accept no bogus patches
          + Use no unstable tools or libraries
          + If it ain't broke, don't fix it
          + If  it  damages usability or maintainability, it's considered
            broke
          + Do not merely deprecate that which deserves to be deleted

   Some noteworthy violations:
     * Nontrivial   workaround   for  platforms  with  obsolete  zoneinfo
       databases
     * The -ns switch is deprecated but deserves to be deleted
     * libtcd painstakingly purged of bogosity

  Harmonics files

   XTide  has  a long history of harmonics file woes and has been through
   four different file formats trying to solve them.

        Readable Extensible Efficient Available
   TXT     X                              X
   XML               X                    X
   SQL               X          X    
   TCD1                         X         X
   TCD2              X          X         X

   XTide 1 used a nice, human-readable text format (harmonics.txt) but it
   was  neither  efficient  nor extensible.  New fields that were really,
   really  necessary  got  wedged in as "hot comments," initiating a long
   downhill slide into architectural chaos.

   Unwisely,  XTide  2  perpetuated  the harmonics.txt format but added a
   new,   extensible   XML   format   for   subordinate   stations   only
   (offsets.xml).   It  was  anticipated  that  one  of  two things would
   eventually  happen:   either  a  reasonably  functional and stable SQL
   database  would become standard issue with the average Unix, obviating
   the  need to avoid that external dependency, or harmonics.txt would go
   away  and  all  stations would be done in extensible XML.  Neither one
   happened.   Migration  to  XML was put off repeatedly because it would
   exacerbate the performance bottleneck.

   Everybody  suffered  with  the  lousy  performance  until  Jan  Depner
   proposed   to  implement  a  binary  format  (TCD).   TCD1  fixed  the
   performance  problem  but  the  extensibility  problem persisted.  New
   fields  could be added with just minor changes to libtcd, but then you
   needed  to  recompile  the world.  Old versions of XTide couldn't read
   new  harmonics  files  after  fields  were  added.   This  had a major
   chilling  effect  on  all  development  that  would  have required new
   fields.

   TCD2   (a   major,   incompatible   revision)  emptied  the  queue  of
   incompatible changes but also added a field whose content is extension
   fields encoded as text.  Adding fields this way is not as efficient as
   adding  new  binary  fields,  but  it  avoids  the  need  to  make  an
   incompatible  revision over small stuff.  The option to add new binary
   fields  and  bump  the  major  rev  remains  open  should  that become
   necessary.

  Known problems

   Lots  of  serious  design problems were fixed in refactorings begining
   with  version  2.7  (early  2004)  and continuing through version 2.9.
   Remaining minor problems:
    1. The interface with X11 is still weird, especially bootstrapping.
    2. The analog tide clock icon caused more problems (with buggy window
       managers) than it was worth.
    3. URLs  assigned  to  prediction  pages  by  the  web  server should
       probably be based on the harmonics file name and the location name
       rather than a transient "row ID."
    4. Constituent  inference  was  patched in via libtcd and maybe could
       have been integrated better.  In theory, you might want to control
       it  on  a  station-by-station  basis  like preferred units, and it
       probably should not require a station reload to turn it on or off.
    5. Graph  and  calendar  modes  are implemented by transient classes.
       These  are  not proper objects, but they are too complicated to be
       implemented with methods alone.

  C++ feature footprint

   At the time XTide 2 was developed, the fancier features of C++ such as
   the  Standard  Template Library (STL) and exceptions did not work in a
   portable  fashion among the commonly available compilers, so their use
   was  avoided.   Similarly,  [5]Qt and other free alternatives to Motif
   were not widely available, so Athena Widgets were used.  The resulting
   interface  may  seem  [6]primitive  by today's standards, but it still
   works.

   By the time of the 2.7 refactorings, the STL appeared to be stable and
   widely   available,   so  standard  templates  were  introduced  where
   appropriate to simplify new code.  Old code was not STLified until the
   Great Cleanup of 2006 (XTide 2.9).

   The long long int data type was introduced in XTide 2.6 as part of the
   changes   to   handle  dates  before  1970  and  after  2037.   Nobody
   complained.

   Streams   were   expunged  from  XTide  2.6  after  compilers  started
   deprecating  XTide's  use  of them.  In XTide, C++ streams did not add
   value  versus  plain  old  C  I/O,  but this is not the case for every
   application.

   The bool data type was introduced in XTide 2.9.

   Exceptions  are  still  not  used,  but  probably  could  be, as those
   compilers  that don't support them don't support the Standard Template
   Library either.

  Coding conventions

   A  uniform  coding  convetion  was imposed in XTide 2.9.  See the file
   CodingConventions.txt included in the distribution tarball.
     _________________________________________________________________

   [7]<- Previous [8]-> Next [9]Contents

References

   1. http://www.flaterco.com/xtide/faq.html
   2. http://www.flaterco.com/xtide/credits.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.trolltech.com/
   6. http://www.catb.org/~esr/jargon/html/S/stone-knives-and-bearskins.html
   7. http://www.flaterco.com/xtide/faq.html
   8. http://www.flaterco.com/xtide/credits.html
   9. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Moonrise over Marginal Way

Bibliography

   Canonical  sources on the NOS tide prediction methodology (including a
   mathematical explanation from first principles in SP98):

     Manual  of  Harmonic  Analysis  and  Prediction  of Tides.  Special
     Publication  No.  98,  Revised  (1940) Edition (reprinted 1958 with
     corrections;  reprinted  again  1994).   United  States  Government
     Printing Office, 1994.

     Computer  Applications  to  Tides  in  the  National  Ocean Survey.
     Supplement  to  Manual of Harmonic Analysis and Prediction of Tides
     (Special  Publication  No.  98).   National Ocean Service, National
     Oceanic   and   Atmospheric   Administration,  U.S.  Department  of
     Commerce, January 1982.

   Those  can  be ordered from NOAA for $5 or $10, depending on the phase
   of the moon.

   Miscellaneous publications available from
   [5]http://www.flaterco.com/xtide/files.html#pubs:

     [6]Tide  and  Current  Glossary.   National  Ocean Service, January
     2000.  Downloaded from [7]NOS, 2003-12-19.

     [8]Tidal  Datums  and their Applications.  NOAA Special Publication
     NOS CO-OPS 1, June 2000.  Downloaded from [9]NOS, 2004-08-27.

     [10]Nathaniel  Bowditch,  LL.D.   The American Practical Navigator:
     An  Epitome  of Navigation.  NIMA Pub. No. 9, Bicentennial Edition,
     2002.  Downloaded from [11]NGA, 2004-09-28.  42 MB.  Chapter 9 is a
     tutorial on tides and currents.

   My sources for X-windows programming reference:

     Kimball, Paul E.  The X Toolkit Cookbook.  Prentice Hall P T R, New
     Jersey, 1995.

     Nye,  Adrian.   Xlib  Programming  Manual.   O'Reilly & Associates,
     Inc., Volume 1, Third Edition, July 1993.

   A  catalog  of  information  on  the  ISO  8601 standard date and time
   notation can be found at
   [12]http://dmoz.org/Science/Reference/Standards/Individual_Standards/I
   SO_8601/.

   iCalendar  format  and  usage is according to [13]RFC 2445 and [14]RFC
   2446, with some hints taken from [15]RFC 2447 (November 1998).

   An  article  about a model-based approach to tide prediction, which is
   completely different from what XTide does, is

     Derek  Goring,  "Computer  Models  Define  Tide  Variability,"  The
     Industrial  Physicist,  v.  7,  n.  5,  October/November  2001, pp.
     14-17.  Available at
     [16]http://www.niwa.co.nz/rc/prog/chaz/news/tidalmodel.pdf       or
     [17]http://www.aip.org/tip/INPHFA/vol-7/iss-5/p14.pdf.

   Michael  Foreman's  publications are a good read if you are interested
   in the Doodson approach to tide prediction.

     Foreman,  M.G.G.,  1977.   Manual  for  Tidal  Heights Analysis and
     Prediction.   Pacific  Marine  Science  Report  77-10, Institute of
     Ocean Sciences, Patricia Bay, Sidney, B.C., 58 pp. (2004 revision).

     Foreman,  M.G.G.,  1978.   Manual  for  Tidal Currents Analysis and
     Predition.   Pacific Marine Science Report 78-6, Institute of Ocean
     Sciences, Patricia Bay, Sidney, B.C., 57 pp. (2004 revision).

     Foreman,  M.G.G.,  and  R.F.  Henry, 1979.  Tidal Analysis Based on
     High  and  Low  Water  Observations.  Pacific Marine Science Report
     79-15,  Institute of Ocean Sciences, Patricia Bay, Sidney, B.C., 36
     pp. (2004 revision).

   Miscellaneous  publications  mentioned by Hugh Casement that I haven't
   read:

     On  the  response  method  of  tide prediction, which is completely
     different  and allegedly better than what XTide does:  Munk, Walter
     H.;  Cartwright,  David  E.:   Tidal  spectroscopy  and prediction.
     Philosophical Transactions of the Royal Society, A 259 (1966).

     An  interesting-sounding publication that Hugh Casement hasn't read
     either:   Horn,  Walter:   Some recent approaches to tidal problems
     (Centre Belge d'Océans, Brussels, year unknown).

     Horn,  Walter:   Tafeln  der  Astronomischen  Argumente  V0 und der
     Korrektionen  j,  v  (Deutsches Hydrographisches Institut, Hamburg,
     1967).

     Doodson, in Proceedings of the Royal Society A.100 (London, 1921).

     Cartwright   and  Tayler,  in  Geophysical  Journal  of  the  Royal
     Astronomical Society 23 (1971).

     Jean Meeus, Astronomical Algorithms, Willmann-Bell.
     _________________________________________________________________

   [18]<- Previous [19]-> Next [20]Contents

References

   1. http://www.flaterco.com/xtide/credits.html
   2. http://www.flaterco.com/xtide/time_t.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/files.html#pubs
   6. ftp://ftp.flaterco.com/xtide/glossary2.pdf
   7. http://www.tidesandcurrents.noaa.gov/pub.html
   8. ftp://ftp.flaterco.com/xtide/tidal_datums_and_their_applications.pdf
   9. http://www.tidesandcurrents.noaa.gov/pub.html
  10. ftp://ftp.flaterco.com/xtide/Bowditch.pdf
  11. http://pollux.nss.nga.mil/pubs/pubs_j_apn_sections.html?rid=187
  12. http://dmoz.org/Science/Reference/Standards/Individual_Standards/ISO_8601/
  13. http://www.flaterco.com/xtide/rfc2445.txt
  14. http://www.flaterco.com/xtide/rfc2446.txt
  15. http://www.flaterco.com/xtide/rfc2447.txt
  16. http://www.niwa.co.nz/rc/prog/chaz/news/tidalmodel.pdf
  17. http://www.aip.org/tip/INPHFA/vol-7/iss-5/p14.pdf
  18. http://www.flaterco.com/xtide/credits.html
  19. http://www.flaterco.com/xtide/time_t.html
  20. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

Appendix A -- Historical predictions and Y2038 compliance

   As of 2002, the average Unix uses a signed 32-bit integer to represent
   time  as a count of seconds since 1970-01-01 00:00:00Z.  The limits of
   that   representation   are   1901-12-13   20:45:52Z   and  2038-01-19
   03:14:07Z.   Some  platforms  instead  use  an unsigned 32-bit integer
   while others already use 64-bit integers.

   XTide  originally  limited  itself  to  the  range 1970 to 2037.  This
   provided  portability  and  reliable  results regardless of the time_t
   representation  and  allowed  Interval  (the  difference  between  two
   timestamps) to be represented using a signed 32-bit integer.  However,
   an  increasing  number  of  requests for historical "past predictions"
   combined  with slow progress in migrating the average Unix platform to
   a time representation capable of surviving year 2038 finally motivated
   the incorporation of a workaround.

   If  XTide  is  compiled with this workaround, time_t is redefined as a
   signed  64-bit integer and the platform's time functions are bypassed.
   Years  from  1  to 4000 are allowed.  However, time zones and daylight
   savings time are sacrificed.  Everything becomes UTC. [4]*

   In  XTide  2.9  and  newer, the workaround can be enabled at configure
   time  using  configure --enable-time-workaround.   The  range of years
   that  is  selectable in timestamp dialogs is automatically expanded to
   1700  to  2100  when  the  time workaround is enabled.  If a different
   range  is  required,  the  definitions  of Global::dialogFirstYear and
   Global::dialogLastYear in Global.cc must be changed manually.

   In  order  to obtain predictions for past and future years, it is also
   necessary  to use a harmonics file that supports those years.  The new
   harmonics  file  harmonics-dwf, rev. 2004-10-05 or later, supports the
   years 1700 to 2100.  If you need to extend the range of years further,
   use the following procedure.
    1. Obtain and build the most recent versions of Congen, Tcd-utils and
       Harmbase2, available at
       [5]http://www.flaterco.com/xtide/files.html.   You  will also need
       to  install  the  version  of  Postgres indicated by the Harmbase2
       instructions.
    2. Obtain  the  most  recent  Postgres database dump of harmonics-dwf
       from  the  same  place  and  load  it:   createdb  harmbase2; psql
       harmbase2 < harmonics-dwf-*.sql.
    3. Export  the database to a new TCD file using the export program of
       Harmbase2,  specifying  whatever years you wanted:  export -b 1700
       -e 2300 harmonics-me.

   If  you  are  using  .txt  and .xml files, you can extend the range of
   years as follows.
    1. Obtain and build the most recent versions of Congen and Tcd-utils,
       available at [6]http://www.flaterco.com/xtide/files.html.
    2. Generate the needed years as explained in the README in the Congen
       distribution.  E.g., congen -a1 -b 1700 -e 2300 < congen_input.txt
       > out.txt.
    3. Using  a  text  editor, edit harmonics.txt and replace the segment
       between  "Begin  congen  output"  and "End congen output" with the
       congen output that you just generated.
    4. Convert the data to TCD format using build_tide_db as explained in
       the README of the Tcd-utils distribution.

   Please  be  aware  that  extrapolating predictions over large spans of
   time may give extremely inaccurate results.  Don't even go there until
   you [7]read this FAQ about it.

   *  The time scale used by the time workaround is not strictly speaking
   UTC  since it does not implement [8]leap seconds, but neither does the
   standard library.  See [9]Limitation #6.
     _________________________________________________________________

   [10]<- Previous [11]-> Next [12]Contents

References

   1. http://www.flaterco.com/xtide/bibliography.html
   2. http://www.flaterco.com/xtide/mincurrents.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/xtide/time_t.html#leap
   5. http://www.flaterco.com/xtide/files.html
   6. http://www.flaterco.com/xtide/files.html
   7. http://www.flaterco.com/xtide/faq.html#57
   8. http://www.boulder.nist.gov/timefreq/pubs/bulletin/leapsecond.htm
   9. http://www.flaterco.com/xtide/bugs.html
  10. http://www.flaterco.com/xtide/bibliography.html
  11. http://www.flaterco.com/xtide/mincurrents.html
  12. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents
   [4]About harmonic constants and sub station corrections
   [5]Change log

Appendix B -- Application of offsets for Min Flood and Min Ebb events

   [6]B.1  Background
   [7]B.2  Secondary Station Adjustments Instructions (NOS)
   [8]B.3  Comparison of old and new results
   [9]B.4  Comparison with published tables

  Background

   XTide distinguishes the following common events for current stations:

   Max Flood           Maximum current in the flood (+) direction.
   Max Ebb             Maximum current in the ebb ( -) direction.
   Slack, Flood Begins Zero current preceding flood.
   Slack, Ebb Begins   Zero current preceding ebb.

   Additionally,  it  distinguishes  two  events  that  are  not  seen as
   frequently:

   Min Flood Minimum current in the flood (+) direction between two Max
   Floods when the current never crosses zero.
   Min Ebb Minimum current in the ebb ( -) direction between two Max Ebbs
   when the current never crosses zero.

   In  XTide 2.8, a change was made to the application of offsets for Min
   Flood and Min Ebb events.

   Event XTide 2.7 time adjust XTide 2.7 current adjust XTide 2.8 time
   adjust XTide 2.8 current adjust
   Min Flood Same as Max Ebb Same as Max Ebb Same as Slack, Flood Begins;
   if null, use Max Flood Same as Max Flood
   Min Ebb Same as Max Flood Same as Max Flood Same as Slack, Ebb Begins;
   if null, use Max Ebb Same as Max Ebb

   This change was made based on a reading of the highlighted sections of
   the National Ocean Service web page quoted below, which was downloaded
   from     [10]http://co-ops.nos.noaa.gov/currents04/t2chelp.html     on
   2004-09-15.

   The  second  highlighted  passage  states  that  no attempt is made to
   predict  the  speed  of the minimum currents.  It would not make sense
   for  XTide to leave these values unadjusted because a very small ratio
   could  cause  the  supposed  maxima  to  have lower amplitude than the
   minimum.  Applying the ratio used for the surrounding maxima will give
   reasonable  looking results as long as the adjustment is only a ratio.
   (Additive adjustments would not produce reasonable results.)
     _________________________________________________________________

           BEGIN NATIONAL OCEAN SERVICE TEXT (highlighting added)
     _________________________________________________________________

                 Secondary Station Adjustments Instructions

   The  publication of full daily predictions is necessarily limited to a
   comparatively small number of stations. These stations are referred to
   as  "reference stations". Tidal current predictions for more than 2500
   other locations can be obtained by applying certain differences to the
   daily predictions for the reference stations.

   These  pages  provide  a  listing  of  the more than 2500 "subordinate
   stations"  for which such predictions can be made, the differences and
   ratios  to  be  used, and a link to the appropriate reference station.
   The  stations  in  the  listing are arranged geographically to make it
   possible  to  find  stations  which  are available for an area you are
   interested in.

   Since  all  tidal  current stations are located offshore, many of them
   are named for the channels, rivers, and inlets they are located in, or
   for  cities, towns, or navigational points they are located near. Some
   personal  knowledge of the area you are interested in may be necessary
   to determine which station(s) are most appropriate for your use.

   Depths:  Although  current  measurements  may  have  been  recorded at
   various  depths in the past, the data listed here for most subordinate
   stations are mean values determined to have been representative of the
   current  at  each location. For that reason, no specific current meter
   depth  for  those stations are given. Beginning with the Boston Harbor
   tidal  current  survey  in 1971, data for individual meter depths were
   published  and  subsequent  new  data  may  be  presented in a similar
   manner.

   Since  most  of  the  current  data  in  these  pages came from meters
   suspended from survey vessels or anchored buoys, the listed depths are
   those  measured  downward  from the surface. Some later data have come
   from  meters  anchored  at  fixed  depths from the bottom. These meter
   positions were defined as depth below chart datum. Such defined depths
   in these pages will be accompanied by the small letter "d".

   Minimum Currents: The user may note that at many locations the current
   may  not  diminish to a true slack water or zero speed stage. For that
   reason,  the  phrases, "minimum before flood" and "minimum before ebb"
   are  used  in these pages rather than "slack water" although either or
   both minimums may actually reach a zero speed value at some locations.

   Maximum  Currents:  Near  the  coast and in inland waters, the current
   increases from a minimum current (slack water) for a period of about 3
   hours  until  the maximum speed or strength of the current is reached.
   The  speed  then  decreases  for  another period of about 3 hours when
   minimum  current  is  again  reached  and the current begins a similar
   cycle  in  the  opposite direction. The current that flows towards the
   coast  or up a stream is known as the flood current; the opposite flow
   is  known  as  the  ebb  current.  Speeds  of the current at reference
   stations  are listed as positive values for floods and negative values
   for  ebbs.  These  pages  list  the  average directions of the maximum
   floods  and  maximum  ebb currents. The directions listed are given in
   degrees, true, reading from 000 at north to 359 and are the directions
   toward which the current flow.

   Differences  and Speed Ratios: These pages contain time differences by
   which  the  user  can  compile  approximate  times for the minimum and
   maximum  current  phases at the subordinate stations. Time differences
   for  those phases should be applied to the corresponding phases at the
   reference   station.  It  will  be  seen  upon  inspection  that  some
   subordinate  stations  exhibit  either  a double flood or a double ebb
   stage,  or  both. In those cases, a separate time difference is listed
   for each of the three flood (or ebb) phases and should be applied only
   to  the  maximum  flood  (or  ebb) phase at the reference station. The
   results  obtained by the application of time differences will be based
   upon  the local time meridian. Differences of time meridians between a
   subordinate  stations  and  its  reference station have been accounted
   for.

   The  speed  ratios  are  used  to  compile approximations of the daily
   current  speeds  at  the  subordinate  stations  and refer only to the
   maximum  floods  and  ebbs. No attempt is made to predict the speed of
   the minimum currents. These ratios are multiplied to the corresponding
   maximum  current phases at the reference station. As mentioned before,
   however,  some  stations may exhibit either a double flood or a double
   ebb, or both. As with time differences, separate ratios are listed for
   each  of the three flood (or ebb) phases and should be applied only to
   the  daily  maximum  flood (or ebb) speed at the reference station. It
   should  be noted that although the speed of a given current phase at a
   subordinate  station  is  obtained  by  reference to the corresponding
   phase at a reference station, the directions of the current at the two
   places   may   differ  considerably.  These  pages  list  the  average
   directions of the maximum current phases at the subordinate stations.

   Example Tidal Current Calculations

   For  Cape  May  Channel,  the time and speed adjustments listed in the
   tables are:
Minimum       Minimum         Speed
Before Flood  Before  Ebb     Ratio
Flood         Ebb           Flood Ebb
-1 14  -1 30  -1 11  -0 45   1.1  1.8

   and  the  reference station is Delaware Bay Entrance. If the times and
   speeds  listed  in column 1 are the minimum and maximum tidal currents
   for a day at Delaware Bay Entrance, column 2 are the time corrections,
   and column 3 are the speed corrections; column 4 will be the predicted
   currents  at  Cape May Channel. These values are computed by adding or
   subtracting  the times in column 1 to the adjustments in column 2; and
   by multiplying the speeds in column 1 by the ratios in column 3.
     (1)                 (2)        (3)         (4)
  Times     Speed                            Times     Speed
0114  0425   1.3    -1 14  -1 30   *1.1    0000  0255   1.4
0736  1055  -1.3    -1 11  -0 45   *1.8    0625  1010  -2.3
1351  1650   1.2    -1 14  -1 30   *1.1    1237  1520   1.3
1958  2316  -1.3    -1 11  -0 45   *1.8    1847  2231  -2.3
     _________________________________________________________________

                      END NATIONAL OCEAN SERVICE TEXT
     _________________________________________________________________

  Comparison of old and new results

   From            [11]http://co-ops.nos.noaa.gov/currents04/tab2pc2.html
   (2004-09-15):
                                                              Minimum       Min
imum         Speed    Direction
                                                              Before Flood  Bef
ore  Ebb     Ratio    At Maximum
Station                                              Depth    Flood         Ebb
           Flood Ebb  Flood Ebb  Reference Station
Admiralty Head, 0.5 mile west of                              -0 31  -0 03  +0
01  -0 07   1.3  1.2   145  025  Admiralty Inlet

   Resulting XTide data set:

   Name          
Admiralty Head, 0.5 mile west of, Washington Current

   Reference     
Admiralty Inlet, Washington Current

   Max time add  
-00:03

   Max level add 
NULL

   Max level mult
1.300

   Min time add  
-00:07

   Min level add 
NULL

   Min level mult
1.200

   Flood begins  
-00:31

   Ebb begins    
+00:01

   NOS  predictions  for  2004-09-08 and 2004-09-09 at reference station,
   from          [12]http://co-ops.nos.noaa.gov/currents04/ADMIRALI.shtml
   (2004-09-15):
    Slack    Maximum   Slack    Maximum   Slack    Maximum   Slack    Maximum
 Slack    Maximum
    Water    Current   Water    Current   Water    Current   Water    Current
 Water    Current
Day  Time  Time  Veloc  Time  Time  Veloc  Time  Time  Veloc  Time  Time  Veloc
  Time  Time  Veloc
     h.m.  h.m.  knots  h.m.  h.m.  knots  h.m.  h.m.  knots  h.m.  h.m.  knots
  h.m.  h.m.  knots

  8         402   -2.3   814  1122    1.5  1449  1801   -1.2        2257   -0.1
  9         508   -2.4   909  1219    1.7  1543  1856   -1.5

   Corresponding XTide results:

   Reference station Sub station (XTide 2.7) Sub station (XTide 2.8)
2004-09-08  4:02 AM PDT  -2.33 knots  Max Ebb
2004-09-08  8:13 AM PDT   0.00 knots  Slack, Flood Begins
2004-09-08 11:22 AM PDT   1.51 knots  Max Flood
2004-09-08  2:48 PM PDT  -0.00 knots  Slack, Ebb Begins
2004-09-08  6:01 PM PDT  -1.22 knots  Max Ebb
2004-09-08 10:57 PM PDT  -0.07 knots  Min Ebb
2004-09-09  5:08 AM PDT  -2.36 knots  Max Ebb
2004-09-09  9:08 AM PDT   0.00 knots  Slack, Flood Begins
2004-09-09 12:19 PM PDT   1.71 knots  Max Flood
2004-09-09  3:42 PM PDT  -0.00 knots  Slack, Ebb Begins
2004-09-09  6:56 PM PDT  -1.47 knots  Max Ebb
2004-09-09 11:22 PM PDT   0.00 knots  Slack, Flood Begins

2004-09-08  3:55 AM PDT  -2.80 knots  Max Ebb
2004-09-08  7:42 AM PDT   0.00 knots  Slack, Flood Begins
2004-09-08 11:19 AM PDT   1.96 knots  Max Flood
2004-09-08  2:49 PM PDT  -0.00 knots  Slack, Ebb Begins
2004-09-08  5:54 PM PDT  -1.47 knots  Max Ebb
2004-09-08 10:54 PM PDT  -0.09 knots  Min Ebb
2004-09-09  5:01 AM PDT  -2.84 knots  Max Ebb
2004-09-09  8:37 AM PDT   0.00 knots  Slack, Flood Begins
2004-09-09 12:16 PM PDT   2.22 knots  Max Flood
2004-09-09  3:43 PM PDT  -0.00 knots  Slack, Ebb Begins
2004-09-09  6:49 PM PDT  -1.77 knots  Max Ebb
2004-09-09 10:51 PM PDT   0.00 knots  Slack, Flood Begins

2004-09-08  3:55 AM PDT  -2.80 knots  Max Ebb
2004-09-08  7:42 AM PDT   0.00 knots  Slack, Flood Begins
2004-09-08 11:19 AM PDT   1.96 knots  Max Flood
2004-09-08  2:49 PM PDT  -0.00 knots  Slack, Ebb Begins
2004-09-08  5:54 PM PDT  -1.47 knots  Max Ebb
2004-09-08 10:58 PM PDT  -0.08 knots  Min Ebb
2004-09-09  5:01 AM PDT  -2.84 knots  Max Ebb
2004-09-09  8:37 AM PDT   0.00 knots  Slack, Flood Begins
2004-09-09 12:16 PM PDT   2.22 knots  Max Flood
2004-09-09  3:43 PM PDT  -0.00 knots  Slack, Ebb Begins
2004-09-09  6:49 PM PDT  -1.77 knots  Max Ebb
2004-09-09 10:51 PM PDT   0.00 knots  Slack, Flood Begins
     _________________________________________________________________

  Comparison with published tables

   When the change in XTide's behavior was made in 2004, the NOS web site
   did not provide calculated predictions at the subordinate stations for
   comparison.   Upon  reviewing  the  issue in 2007 (at which time those
   predictions  were  available),  it was found that the published tables
   did neither of the behaviors that were implemented in XTide.

   CAPTION: Time offsets applied to Min Ebb event

   XTide 2.7     XTide 2.8      NOS 2007
     Flood   Minimum Before Ebb   Ebb

   Whereas  the behavior of the published tables seemed to be in conflict
   with  the  [13]Secondary  Station  Adjustments  Instructions,  it  was
   resolved not to change the behavior of XTide at that time.

    Reference station

   NOS table copied from
   [14]http://tidesandcurrents.noaa.gov/get_predc.shtml?year=2007&stn=603
   0+Admiralty+Inlet&fldavgd=179&ebbavgd=003&footnote= 2007-02-24

        Admiralty Inlet
   Predicted Tidal Current     March, 2007
   Flood Direction, 179 True.  Ebb (-)Direction, 003 True.
   NOAA, National Ocean Service

     Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current
   Day Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots
   12 0049 0347 -0.9   0825 -0.1   1458 -2.4 1917 2229 +1.5
   13 0207 0512 -1.0   0948 -0.2   1610 -2.4 2019 2335 +1.8

   Comparable XTide output, using harmonics-rmk-20040615.tcd
   tide -l"admiralty inlet" -b"2007-03-12 00:00" -e"2007-03-14 00:00" -mc
   -empSsMm -tf"%H%M" -fh

   Day Slack Flood
   Slack
   Ebb Slack Flood
   Slack
   Mon 12 0048 0347 -0.93 kt
   0824 -0.08 kt
   1457 -2.41 kt 1916 2229 1.52 kt
   Tue 13 0206 0512 -1.04 kt
   0948 -0.18 kt
   1610 -2.45 kt 2018 2335 1.75 kt

    Subordinate station

Name             Agate Pass, North End of, Washington Current
Reference        Admiralty Inlet, Washington Current
Min time add     -0:59
Min level add    NULL
Min level mult   0.700
Max time add     -1:00
Max level add    NULL
Max level mult   0.800
Flood begins     -1:28
Ebb begins       -0:18

   NOS table copied from
   [15]http://tidesandcurrents.noaa.gov/get_predc.shtml?year=2007&stn=603
   0+Admiralty+Inlet&secstn=Agate+Passage,+north+end&sbfh=%2D1&sbfm=28&fl
   dh=%2D1&fldm=00&sbeh=%2D0&sbem=18&ebbh=%2D0&ebbm=59&fldr=0.8&ebbr=0.7&
   fldavgd=230&ebbavgd=032&footnote= 2007-02-24

        Agate Passage, north end
   Predicted Tidal Current      March, 2007
   Flood Direction, 230 True.   Ebb (-)Direction, 032 True.
   NOAA, National Ocean Service

     Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current
   Day Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots
   12 0031 0248 -0.6   0726 -0.1   1359 -1.7 1749 2129 +1.2
   13 0149 0413 -0.7   0849 -0.1   1511 -1.7 1851 2235 +1.4

   Comparable XTide output, using harmonics-rmk-20040615.tcd
   tide  -l"Agate  Pass,  North End of, Washington Current" -b"2007-03-12
   00:00" -e"2007-03-14 00:00" -mc -empSsMm -tf"%H%M" -fh

   Day Slack Flood
   Slack
   Ebb Slack Flood
   Slack
   Mon 12 0030 0248 -0.65 kt
   0806 -0.06 kt
   1358 -1.69 kt 1748 2129 1.21 kt
   Tue 13 0148 0413 -0.73 kt
   0930 -0.13 kt
   1511 -1.71 kt 1850 2235 1.40 kt
     _________________________________________________________________

   [16]<- Previous [17]-> Next [18]Contents
   [19]About harmonic constants and sub station corrections
   [20]Change log

References

   1. http://www.flaterco.com/xtide/time_t.html
   2. http://www.flaterco.com/xtide/pound_to_fit.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/xtide/harmonics.html
   5. http://www.flaterco.com/xtide/changelog.html#2.8
   6. http://www.flaterco.com/xtide/mincurrents.html#background
   7. http://www.flaterco.com/xtide/mincurrents.html#instructions
   8. http://www.flaterco.com/xtide/mincurrents.html#oldnew
   9. http://www.flaterco.com/xtide/mincurrents.html#tables
  10. http://co-ops.nos.noaa.gov/currents04/t2chelp.html
  11. http://co-ops.nos.noaa.gov/currents04/tab2pc2.html
  12. http://co-ops.nos.noaa.gov/currents04/ADMIRALI.shtml
  13. http://www.flaterco.com/xtide/mincurrents.html#instructions
  14. http://tidesandcurrents.noaa.gov/get_predc.shtml?year=2007&stn=6030+Admiralty+Inlet&fldavgd=179&ebbavgd=003&footnote=
  15. http://tidesandcurrents.noaa.gov/get_predc.shtml?year=2007&stn=6030+Admiralty+Inlet&secstn=Agate+Passage,+north+end&sbfh=%2D1&sbfm=28&fldh=%2D1&fldm=00&sbeh=%2D0&sbem=18&ebbh=%2D0&ebbm=59&fldr=0.8&ebbr=0.7&fldavgd=230&ebbavgd=032&footnote=
  16. http://www.flaterco.com/xtide/time_t.html
  17. http://www.flaterco.com/xtide/pound_to_fit.html
  18. http://www.flaterco.com/xtide/xtide.html#contents
  19. http://www.flaterco.com/xtide/harmonics.html
  20. http://www.flaterco.com/xtide/changelog.html#2.8

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   [1]<- Previous [2]-> Next [3]Contents
   [4]Modes and formats
   [5]FAQ

Appendix C -- Making calendars fit onto a single page

  Get rid of unwanted information

   Regardless  of  which  format you are using, having extra stuff in the
   calendar  that you don't want isn't going to help.  If you are using a
   web  page  somewhere,  look for options that allow you to suppress sun
   and  moon  events or control the formatting of timestamps.  If you are
   using  XTide  directly,  you  do  this using the eventmask and timefmt
   settings.   The  following examples assume command line usage, but you
   can  change  settings  in  several  other  ways.   See [6]settings for
   details.

   To  get  rid  of unwanted columns for sun and moon events, use the -em
   command  line  switch  to set an event mask.  E.g, to suppress all sun
   and  moon events, set the event mask to the value pSsMm.  p = phase of
   moon, S = sunrise, s = sunset, M = moonrise, m = moonset.

   To  get  rid  of  unwanted  verbosity in timestamps (AM/PM and/or time
   zone),  use the -tf command line switch to set the time format string.
   E.g.,  to  reduce  it to four digits of 24-hour notation, set the time
   format  string to %H%M.  To keep AM/PM but lose the time zone, set the
   time format string to %l:%M %p.

  Scale down HTML

   If the calendar that you want to print is on a web page, the next step
   is  to  set up your print scaling to make it fit on the page without a
   lot  of  ugly  text  wrapping.  The process for doing this is slightly
   different depending on your browser and operating system.

    Firefox 1.5.0.1 Linux

   Access the print scaling menu via File -> Page Setup.  On the Format &
   Options  tab,  unselect  Shrink  To  Fit  Page  Width  and  specify an
   arbitrary  shrink factor.  Try various shrink factors and see how they
   look in File -> Print Preview.  Print when you find one you like.

   The  Format  &  Options  tab also lets you choose between Portrait and
   Landscape  printing,  which  can  be helpful depending on whether your
   calendar is really long or really wide.

    Firefox 1.5.0.1 Windows XP

   Do  File  -> Print Preview.  Use the controls at the top of the window
   to  select  Portrait  or Landscape printing and to scale down the HTML
   until it fits nicely on a page.  When ready, select Print.

    Internet Explorer 6 Windows XP

   Internet Explorer 6 does not support print scaling.  No wonder so many
   Windows users had trouble printing calendars!  Doh!  (Smack forehead.)

   Some  Windows  printer  drivers  add  an option for print scaling on a
   buried menu, but what that does is not what you need.

    Internet Explorer 7 Windows XP

   The  following instructions are based on Microsoft's documentation.  I
   cannot  test  these  instructions because IE7 installation fails on my
   PC.

    1. Click  the  arrow to the right of the Print button, and then click
       Print Preview.
    2. Pull  down the print size menu ( Shrink To Fit ) and try different
       options until the calendar fits nicely on a page.
    3. When ready, click on the tiny printer icon to print.

  Get serious--use LaTeX

   The  problem  with  printing  calendars from HTML is that HTML doesn't
   know  anything  about  typesetting  printed  documents.   HTML  has no
   concept  of  pagination.   Whether  the  result ends up on one page or
   three when you print it was never supposed to be a concern.

   The  right language to use in this case is LaTeX.  Like HTML, LaTeX is
   a markup language, but it is all about typesetting printed documents.

   XTide  can generate calendars in LaTeX format.  These can be converted
   to PDFs using pdflatex, and those PDFs can then be printed on any size
   paper using Acrobat Reader.

   If  you  are using XTide through a web page, you just have to hunt for
   an option to generate a PDF and hope that there is one.

   The  process  to  generate  and view a PDF from the command line is as
   follows:
bash-3.00$ tide -l"Location Name" -mc -fl -b"Start Time" -e"End Time" > cal.tex
bash-3.00$ pdflatex cal.tex
bash-3.00$ acroread cal.pdf

   The  default  page  geometry in LaTeX mode is probably not optimal for
   making  your calendar look nice.  Experiment with different values for
   pageheight  (-ph 420) and pagewidth (-pw 297) until the calendar looks
   nice  in  PDF.  Do not worry that the shape of the pages in the PDF is
   not what you have in your printer.

   [7]example of nicely formatted calendar

   When you are happy with the look of the PDF, do the following to print
   it.

    Acrobat Reader 7.0 Linux

   Use  the File -> Print Setup menu of Acrobat Reader to select Portrait
   or Landscape printing, then on the File -> Print menu check off Shrink
   oversized pages to paper size and Expand small pages to paper size.

   Issue:  I have experienced disappearing lines when printing via the HP
   DeskJet  5550 driver of CUPS 1.1.23.  This problem does not occur when
   printing  under Windows XP, so clearly there is some print option that
   I am missing.

    Acrobat Reader 7.0 Windows XP

   Use  the File -> Print Setup menu of Acrobat Reader to select Portrait
   or  Landscape  printing,  then  on the File -> Print menu, change Page
   Scaling to Fit to Printer Margins.
     _________________________________________________________________

   [8]<- Previous [9]-> Next [10]Contents
   [11]Modes and formats
   [12]FAQ

References

   1. http://www.flaterco.com/xtide/mincurrents.html
   2. http://www.flaterco.com/xtide/xtide1diff.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/xtide/modes.html
   5. http://www.flaterco.com/xtide/faq.html#onepage
   6. http://www.flaterco.com/xtide/settings.html
   7. http://www.flaterco.com/xtide/BarHarbor.pdf
   8. http://www.flaterco.com/xtide/mincurrents.html
   9. http://www.flaterco.com/xtide/xtide1diff.html
  10. http://www.flaterco.com/xtide/xtide.html#contents
  11. http://www.flaterco.com/xtide/modes.html
  12. http://www.flaterco.com/xtide/faq.html#onepage

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   [1]<- Previous [2]-> Next [3]Contents

Icon Differences from XTide 1

   XTide  2 is a complete redesign of XTide 1.  There are too many subtle
   improvements to list them all, but here are the not so subtle ones:
     * New interactive user interface for X windows client
     * Integrated web server now provided in distribution
     * Simpler, better command line interface
     * Handles multiple harmonics files transparently
     * Subordinate  stations  are  now stored in an external database and
       are expanded to handle all known styles of offsets
     * Hydraulic currents are fixed
     * Removed useless options and modes
     * Added sun and moon information (by popular demand...)
     * Fast, efficient binary format for harmonics data

   These are the non-obvious things you must know in order to migrate:
    1. The  environment  variable  HFILE is no longer used to specify the
       harmonics file; instead, HFILE_PATH is used:

export HFILE_PATH=/usr/local/share/xtide/harmonics.tcd

       If HFILE_PATH is not set, XTide looks for the file "harmonics.tcd"
       in the default directory.
    2. XTide  now  has  its  own built-in icon.  Remove any icon settings
       that you made in your window manager init files.
    3. You  may  no  longer  use anonymous units in harmonics files.  The
       units  must  be  one  of  the recognized alternatives.  These are:
       feet, meters, knots, knots^2 (for hydraulic currents).  If you are
       still  using  an  ancient harmonics file that contains no units or
       "bogo-knots,"  then  shame  on  you.   It's  high  time  that  you
       upgraded.
     _________________________________________________________________

   [4]<- Previous [5]-> Next [6]Contents

References

   1. http://www.flaterco.com/xtide/pound_to_fit.html
   2. http://www.flaterco.com/xtide/quickinst.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/xtide/pound_to_fit.html
   5. http://www.flaterco.com/xtide/quickinst.html
   6. http://www.flaterco.com/xtide/xtide.html#contents

