Global Positioning System (GPS)

A satellite-based system that provides positioning and navigation information. By triangulation of signals from three of the satellites, a receiving unit can pinpoint its current location anywhere on earth to within a few meters. Use of at least three satellites is necessary to calculate a two-dimensional position (latitude and longitude) and track movement. Four or more satellites are needed to determine a three-dimensional position (latitude, longitude, and altitude). GPS uses the World Geodetic System (WGS 84) as its reference coordinate system.