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Mobile Location Services: The Definitive Guide by Andrew Jagoe

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GPS

The GPS is a passive, satellite-based navigation system maintained and operated by the U.S. Department of Defense. Its primary purpose is to provide global positioning and navigation for land-, sea-, and air-based tactical forces—but it has also been made available for commercial use. Until May 2000, a selective availability mask distorted the satellite clock signals to reduce the accuracy available for commercial applications. Now that this has been removed, the accuracy of GPS is between 5 and 40 meters, provided the GPS receiver has a clear view of the sky.

How GPS Works

Absolute positioning is the fastest and most common use of GPS for real-time navigation (see Figure 5.4). GPS receivers are range measurement devices that measure the ...

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