A Brief Introduction to XTide
XTide is free software for predicting tides. If you live on the water, then you're already convinced that it's the coolest program ever written. But if you're stuck inland, like 99% of the human population, you may still find it to be an interesting and possibly educational toy. In fact, I originally wrote it to ease the pain of long hours in a land-locked, windowless office.
XTide can provide tide predictions in a wide variety of graphic and text formats. It can also act as an on-screen tide clock, showing the current time and water level at the location of your choice.
It was developed entirely under Linux, but all flavors of Unix are supported. Ports to Macintosh, DOS, MS-Windows and OS/2 also exist, supported by their respective maintainers.
Since XTide's release in Summer 1995, web sites offering tide predictions have appeared everywhere. It is probably a safe bet that the majority of XTide users have used it only through a web page. Dean Pentcheff's page (http://tbone.biol.sc.edu/tide/) is an example, offering tide predictions for many locations world-wide. However, if you look around, you will find that many coastal cities have their own XTide pages offering local tide information. [One example of this is our own page for Pacific Beach, Washington at http://www.a42.com/grays/PB/. —Pub]
XTide is released under the GNU Public License and comes with no warranty. It is an excellent tool for visualizing tide predictions, but don't ever depend on it for navigation or use it where an error could be dangerous. XTide's predictions are only as good as its database of tide information, and that was built up almost entirely by scavenging the Net. Always verify the output against predictions published by NOAA or a similar agency before taking any risks.
The primary site for the XTide source distribution is universe.digex.net/~dave/files/. Only HTTP access is permitted (no anonymous FTP). However, that web page contains full instructions for downloading via HTTP and even provides a program, http_get, to make it easier.
You will need to get at least two files: an XTide source distribution and a harmonics file. The harmonics file is the database of tide information that XTide uses to predict the tides. The default harmonics file, harmonics, contains data for many U.S. and British Columbia locations, as well as a fair number of assorted locations world-wide. There is another harmonics file, harmonics.canadian, which contains data for over 1,000 Canadian locations.
Generally, there will be two source distributions available: a stable version and a development version. The development version will have “dev” in the file name. XTide follows an open development process, much like the Linux kernel, with every new feature immediately available to those brave enough to run it.
While XTide installation is not fully automatic, there is nothing especially difficult about it. The following is taken from the XTide README, simplified by the assumption that we have a typical Linux system:
Copy the harmonics file to the place that you have decided to put it (e.g., /etc/harmonics), gunzip it, and chmod 644.
Edit the #defines in config.h to specify the location and name of the harmonics file and the default location for which to show tides. The location you specify must be in the harmonics file. NOTE: The environment variables LOCATION and HFILE override the values specified in config.h, so you might just want to set these in /etc/profile instead.
xmkmf; make depend; make.
Copy the xtide executable into /usr/X11R6/bin.
Copy xtide.man to /usr/man/man1/xtide.1 and chmod 644.
Copy xtide.xpm into /usr/include/X11/pixmaps (mode 644) and change your window manager config file to use that icon for windows whose names start with “XTide”. The syntax to do this in fvwm (system.fvwmrc) is:
Style "XTide*" Icon xtide.xpm
XTide is controlled almost entirely by command line switches. Pull-down menus and other user-interface niceties may be added in future versions; thus far it's been a challenge just keeping up with the more urgent feature requests.
XTide has way too many command line switches. Everyone seems to want different things from a tide program, and I have attempted to keep everyone happy. As a result, the default modes are very simple and boring, and you need to supply the switches to turn on any fancy features you may want. The XTide README can help with this; you can also type xtide -help to get a listing of the switches.
The default mode for XTide is tide clock, with no fancy options enabled. To get it to look like the picture, you need at least the following switches:
-now Show current time in tide clock. -hinc Label the tide height tick marks with default increment. -tinc Label the time tick marks with default increment. -hairy "Hairy" tide clock mode, showing slice of tide graph.
In order to get a different location and/or the time zone for that location, you will need these:
-list List all supported locations. -location Specify the location for which to predict tides -loctz Use their time zone, not mine.
<f“Courier”>-location random<f$> will cause XTide to choose a location at random.
If you are not interested in keeping a tide clock on your desktop, the next most interesting mode will probably be graph mode. For that, you will need these switches:
-graph Specify graph mode. -gstart Specify the starting time for graphs and listings.
The format for the time stamps given to -gstart is YYYY:MM:DD:HH:MM. For example, half past midnight, June 1, 1995, is 1995:06:01:00:30.
By generating tide graphs for various locations, you will quickly get a feel for the different kinds of tides different places have. Many people are surprised to find out that not all places have two high tides and two low tides each day. Some places, like Bayou Rigaud, Louisiana, have only one high and one low tide per day; other places, like Brunswick, Maine, can have four of each! The latter are known as quarter-diurnal tides; the former (diurnal tides) are also interesting in that they will sometimes flatline, showing almost no tidal activity for 24 hours or more.
XTide supports many other modes, including simple ASCII text listings of tides, tide calendars, PPM and GIF output, and even Java-based tide graphs. It also has many options of special interest to folks on the water, such as to apply offsets for secondary tide locations, or to find the times at which the water goes above or below a specific tide level. Most of these options are explained in greater detail in the XTide README.
|Happy Birthday Linux||Aug 25, 2016|
|ContainerCon Vendors Offer Flexible Solutions for Managing All Your New Micro-VMs||Aug 24, 2016|
|Updates from LinuxCon and ContainerCon, Toronto, August 2016||Aug 23, 2016|
|NVMe over Fabrics Support Coming to the Linux 4.8 Kernel||Aug 22, 2016|
|What I Wish I’d Known When I Was an Embedded Linux Newbie||Aug 18, 2016|
|Pandas||Aug 17, 2016|
- Happy Birthday Linux
- Downloading an Entire Web Site with wget
- ContainerCon Vendors Offer Flexible Solutions for Managing All Your New Micro-VMs
- Updates from LinuxCon and ContainerCon, Toronto, August 2016
- New Version of GParted
- What I Wish I’d Known When I Was an Embedded Linux Newbie
- NVMe over Fabrics Support Coming to the Linux 4.8 Kernel
- Tor 0.2.8.6 Is Released
- A New Project for Linux at 25
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide