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How GPS Works

by: Anne King

Global Positioning System (GPS) is a navigational aid originally developed for the military. The system simply receives signals. It is the applied technology that gives the GPS its versatility.

If you have ever used map and compass, you will understand a little about how the GPS
works. In order to find your position on a map, you need to have three points of
reference. The intersecting line from the reference points is where you are. Map and
compass work uses triangulation (bearings), GPS uses trilateration (distances) to calculate location. Satellites orbiting the earth emit unique signals that can be received by a GPS. The GPS software interprets the signal, identifying the satellite that it came from, where it was located, and the time that it took for the signal to reach the system. Once the receiver has both time and distance it begins to determine position.

Three satellites provide the intersection point and the fourth is used to check that the positioning is accurate. Accuracy depends upon the synchronization of atomic clocks in the satellites with the clock in the GPS system. Although the clock in the GPS is not atomic, utilizing the fourth satellite gives it that functionality as the internal clock adjusts itself to correct any discrepancy discovered.

GPS has gone far beyond its initial military application. Drivers can find their way
through city streets, long distance trekkers use the technology to cross unfamiliar terrain, mariners and pilots use GPS enhanced data to cross the seas and skies.

In--vehicle GPS can be integrated into the car entertainment system or can be installed as a removable device. These systems need to tell the driver where he/she is and how to
reach their destination. The information includes road directions plus relevant features along the way such as rest stops, gas stations, points of interest, etc. Auto GPS uses voice commands so that the driver can concentrate on the road.

Hikers and trekkers use similar technology, but normally without the inclusion of road
systems on their devices. Mapping software defines the territory that the hiker will
encounter. The user can enter waypoints (points of reference) so they can return using the same route. They can add points of interest such as water sources, possible campsites, and other items of interest on their trail. However, the portability demanded by hikers will also limit the functionality of the system as small screens mean that some detail will be lost.

It is GPS technology that is used to track individuals on home arrest, to trace missing
pets, stolen vehicles, and missing people. Small systems can be incorporated into pet
collars and wristwatches. As long as the receiver is active, it can be found.

Marine and aviation GPS units are sophisticated and specialized. The principles involved are the same as any standard system; the software is much more highly developed.

Any fisherman, who is using a fish finder on his boat, is using a GPS that is enhanced by
sonar and tracking devices. Units have been developed for use on float tubes also -– as
GPS technology advances, the systems become more and more compact and their uses
more and more extensive.

If you are considering purchasing a GPS, make sure that it can be updated easily. This is especially true if you buy a multi--function GPS or one that is used where conditions change regularly. An in--vehicle GPS soon loses its usefulness if it is not updated as road systems change.

Updates vary according to the device being used. They can come in CD/DVD packages
or as computer downloads. The user can purchase maps specific to the area in which the GPS will be used or a range of maps and routes. These are available from GPS software companies who will charge proportionally to the sophistication of the software.

GPS units vary in price according to their usefulness. It is possible to buy units for less than one hundred dollars to units costing more than one thousand dollars. What your needs are will be a factor in the cost of your unit. If you are a backpacker then portability is a major consideration. If you are a trucker, you need to be able to find a delivery point as quickly and conveniently as possible. Whatever device you go for, cost is generally related to quality. Buy the best you can afford.

About the author:
Anne King is a sports and recreation writer in Boise, Idaho. For more GPS information, visit Maps GPS Info.com which provides practical information on GPS and maps that everyone can use. The website includes product reviews and a maps/GPS glossary.