Rather than measure direction, however, a GPS receiver uses the time it takes for each satellite's beacon to reach it and calculates a distance.
Because radio waves travel at the speed of light, the receiver divides the time the signal takes to reach the receiver by the speed of light (186,000 miles per second) and determines the distance. These distances can be used to form spheres around the satellites that will intersect at a specific position just as the lines drawn from the mountain peaks will intersect at a specific position.
Understanding Gps Measurements
Assume a GPS receiver is sitting in Nebraska. Once activated it begins to collect signals from GPS satellites 1, 2, 3, 4, 5, and 6. The distance to each satellite can be determined using the distance formula d = rt (distance, d, equals rate, r, multiplied by time, t, or distance equals velocity multiplied by time). Although all the satellites are 10,900 miles from the surface of the Earth, the distances to each one will vary according to its position in orbit. For example, all the street lights in a city may be 15 feet in the air but they are not all 15 feet from a specific point in the city.
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