What is GPS?

The Global Positioning System

The Global Positioning System (GPS) is a navigation and precise positioning tool. Developed by the Department of Defense in 1973, GPS was originally designed to assist soldiers and military vehicles, planes, and ships in accurately determining their locations. GPS constellation consists of 24 satellites orbiting the Earth in 12-hour circular orbits. Divided into six groups of four, each group is assigned a different orbital path to make sure that they can be detected from anywhere on the Earth's surface.

A GPS receiver calculates its position by measuring the distance between itself and three or more different GPS satellites. Measuring the time delay between transmission and reception of each GPS microwave signal gives the distance to each satellite, since the signal travels at a known speed. These signals also carry information about the satellites' location and general system health (known as almanac and ephemeris).

By determining the position of, and distance to, at least three satellites, using atomic clocks, the receiver can compute its position using triangulation. Receivers typically do not have perfectly accurate clocks and therefore track one or more additional satellites to correct the receiver's clock error.