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Global Positioning System (GPS)

Coordinates of objects, people, or places represent fundamental information required for any GIS. Since achieving initial operational capability in December 1993, the Global Positioning System (GPS) has allowed users to determine position easily, quickly, and cheaply. With the global market predicted to top $20 billion by 2008, GPS has rapidly become the primary technique for location determination for GIS-related applications.

GPS is a military system run by the U.S. Department of Defense, which maintains a constellation of 24 satellites (plus several spares) at an altitude of about 20,000 km. The satellites transmit signals on L-band frequencies onto which timing codes are modulated. A receiver with knowledge of these codes can measure the time taken for a signal to arrive from any particular satellite and, hence, by ...

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