GPS- global positioning system is a space age version of triangulation. Originally developed for military use. GPS has three components satellites orbiting Earth, master control stations around the world, and receivers installed in locations ranging from naval destroyers to private golf carts.
In the US GPS system, two dozen, Navstar satellites orbit the planet every 12 hours, following six different orbits. Three additional satellites orbit as backup. The satellites contain atomic clocks that send precise times with each signal. The control stations monitor the satellites, using remote controlled on board thrusters to manage their positions.
When a GPS user on land or sea calls for location information, signals pass from orbiting satellites to that user’s receiver. The length of time taken by the transmissions- usually a fraction of a second – helps determine distance to a point on an imaginary sphere, and the user’s latitude and longitude can be calculated by using the mathematics of triangulation.
GPS signals are broadcast on two different frequencies, one for military use and one for civilian use. Civilian augmentation can provide precise location to within 0.4 of an inch.