Motorola L3393 Owner's Manual page 55

stations. GPS uses these "man-made stars" as reference points to calculate
positions accurate to a matter of meters. In fact, with advanced forms of
GPS you can make measurements to better than a centimeter! In a sense it
is like giving every square meter on the planet a unique address.
Here's how GPS works in five logical steps:
The basis of GPS is "triangulation" from satellites.
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l To "triangulate," a GPS receiver measures distance using the travel
time of radio signals.
l To measure travel time, GPS needs very accurate timing that it
achieves with some tricks.
Along with distance, you need to know exactly where the satellites
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are in space. High orbits and careful monitoring are the secret.
Finally you must correct for any delays the signal experiences as it
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travels through the atmosphere.
Five broad categories of GPS application:
Location – determining a basic position
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l Navigation – getting from one location to another
Tracking – monitoring the movement of people and things
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l Mapping – creating maps of the world
Timing – bringing precise timing to the world
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Operating Your Computer 2-25