The latitude and the longitude can be determined using three satellites. In order to calculate the altitude, a fourth satellite is needed. Aeroplanes require an additional satellite.
GPS applications continue to grow in land, sea, air, and space navigation. The ability to enhance safety and to decrease fuel consumption will make GPS an important component of travel in the international airspace system. The GPS system is also extremely accurate, the differential GPS provides a horizontal position accurate to about 3 m. Airplanes will use GPS for landing at fogbound airports. Automobiles will use GPS as part of intelligent transportation systems. Emerging technologies will enable GPS to determine not only the position of a vehicle but also its altitude.
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