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How GPS Works
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.
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