GPS OVERVIEW
A GPS receiver is a simple range-measurement device. Distances are
measured between the receiver antenna and the satellites, and the position is
determined from the intersections of the range vectors. These distances are
determined by a GPS receiver, which precisely measures the time it takes a
signal to travel from the satellite to the station. This measurement process is
similar to that used in conventional-pulsing marine-navigation systems and
in phase-comparison EDM land-surveying equipment.