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GPS
Overview
The Sky's The Limit
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What
is GPS?
GPS, or Global Positioning System, is a satellite-based
navigation system developed by the U.S. Department of Defense to provide a consistent, accurate method of simplifying navigation.
It was originally designed for the military, however, it provides both commercial and recreational users 24 hour, worldwide
navigation coverage with a possible accuracy to 15 meters (49 feet). Like any other
method of navigation, you should not rely solely on your GPS. You should use every method of navigation available
and compare the results to make sure that you are where you think you are.
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What
are the Advantages of GPS Navigation?
For centuries, mariners have been searching for an accurate
method of traveling the world's waterways. From celestial navigation to lorans and SatNav, each system has had its problems
with weather, range and reliability.
GPS takes navigation to a higher level by providing accurate position and course information,
anywhere in the world, regardless of the weather or your proximity to land. The accuracy and coverage of GPS navigation can
help make your boating safer, smarter and more efficient wherever you may travel.
The GPS is a powerful tool. To better understand its operation
and capabilities, it may be helpful to review the basic terms and concepts explained below.
Navigation is the process of traveling from one place to another and knowing where you are
in relation to your desired course.
Position is an exact, unique location based on a geographic coordinate system. Marine navigation
is based on the latitude/longitude coordinate system.
Meridians of longitude are a set of imaginary circles around the earth that pass through the
north and south poles. Longitude describes position in terms of how many degrees it is east or west of the Prime Meridian
(0° Longitude which runs through Greenwich England).
Parallels of latitude are another set of imaginary circles that are perpendicular to the earth's polar
axis. Latitude describes position in terms of how many degrees it is north or south of the equator (0° Latitude).
A waypoint marks
an exact position fix so it can be recalled for future use. The GPS lets you mark waypoints electronically, without physical
landmarks.
Bearing is a compass direction to a particular destination (waypoint) from your present
position.
Track is a compass direction representing your course over ground or course made good.
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How
Does GPS Work?
GPS Navigation uses orbiting satellite signals to determine
your position. These satellites continually send out radio signals containing precise position and time information back to
earth. By knowing the position of 3, 4 or more of these satellites and calculating various time differences between the transmitted
signals, your GPS receiver can determine its present position anywhere on earth. Once underway, your GPS continually updates
your position and provides speed and track information.
What information do I get from a GPS?
Various manufacturers make
GPS's and some have more features than others but all give basically the same information. Almost all of them have graphic
displays and some even have a cartographic feature which allows you to see your location on an electronic chart. If you are
going for a fixed mounted GPS rather than a handheld portable, I would vote for a model that does support electronic charts.
This provides yet another way of checking your position, especially if you are in site of land or an object on the chart.
You should expect your GPS to accept waypoints (where
you want to go) and routes (a series of waypoints leading to your final destination). Once you have input a waypoint the GPS
will calculate your current position and give you, at minimum, the following information:
- A course to steer to the waypoint
(continually updated)
- The distance to the waypoint
(continually updated)
- Once underway your speed (continually
updated)
- The time it will take to get
to the waypoint at your current speed (continually updated)
- Turn, Steer or Off-Course Error
-- the GPS should tell you when you are off course and what direction to turn to get back on course.
- Various alarms should be available
such as:
- an arrival alarm which sounds
when approaching a waypoint
- a proximity alarm which sounds
when you come within a preset distance of any of several waypoints, regardless of whether they are your destination
- an anchor alarm which sounds
when you travel more than a preset distance from a waypoint
- an off-course alarm which sounds
whenever you are exceeding a preset distance from your intended course
With all this information could I share it with
other electronics?
The ability of a GPS to share information with an autopilot,
radar, or plotter adds to the utility and power of the device. Just think of having the ability to feed your autopilot information
on a multi-leg route to a favorite diving spot and having your boat guide itself safely there, leaving you free to ready the
equipment, monitor the radar, and stand watch.
Should I buy one?
It is my opinion that GPS receivers are like your American
Express card (Don't leave home without it). You can get a portable GPS receiver for under Lm100.00 and fixed mounted models
start at under Lm300.00 but go up rapidly from there when you get into the ones with electronic charts. Is it worth Lm100.00
to know your position in any weather, anywhere on earth, within just a few feet? Like the computer revolution, the GPS revolution
is a great example of increasing features, increasing user friendliness, and decreasing costs.
Once again: You
should never rely on only one method of navigation, especially if you will be out of sight of land. |
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DIG DEEPER
MORE DETAILED INFO ON GPS
Extremely interesting
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