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The Garmin Nüvi Pocket Guide by Jason D. O’Grady

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The Basics of GPS

For the magic of GPS to happen, a couple of planets—or, more accurately, satellites—have to align. A GPS receiver on the ground acquires tracking signals from at least three orbiting satellites and uses the data it receives to establish the longitude and latitude of the receiver. If the receiver can acquire four or more GPS signals, it can also determine the altitude.

The U.S.-developed GPS is used worldwide for navigation (air, marine, and land), mapmaking, and surveying; it also has numerous commercial and hobby applications. Due to its high level of accuracy, GPS is also used as a time reference for computer networks. Other satellite navigation systems that are being developed include GLONASS (Russia), Galileo ...

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