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GPS Last modified: Thursday, March 02, 2006

Short for Global Positioning System, a worldwide MEO satellite navigational system formed by 24 satellites orbiting the earth and their corresponding receivers on the earth. The satellites orbit the earth at approximately 12,000 miles above the surface and make two complete orbits every 24 hours. The GPS satellites continuously transmit digital radio signals that contain data on the satellites location and the exact time to the earth-bound receivers. The satellites are equipped with atomic clocks that are precise to within a billionth of a second. Based on this information the receivers know how long it takes for the signal to reach the receiver on earth. As each signal travels at the speed of light, the longer it takes the receiver to get the signal, the farther away the satellite is. By knowing how far away a satellite is, the receiver knows that it is located somewhere on the surface of an imaginary sphere centered at the satellite. By using three satellites, GPS can calculate the longitude and latitude of the receiver based on where the three spheres intersect. By using four satellites, GPS can also determine altitude. GPS was developed and is operated by the U.S. Department of Defense. It was originally called NAVSTAR (Navigation System with Timing and Ranging). Before its civilian applications, GPS was used to provide all-weather round-the-clock navigation capabilities for military ground, sea, and air forces. GPS has applications beyond navigation and location determination. GPS can be used for cartography, forestry, mineral exploration, wildlife habitation management, monitoring the movement of people and things and bringing precise timing to the world. Sponsored listings GPS Systems - Be fleet smart with GPS. Download a free Networkfleet white paper about how to optimize maintenance and diagnostic information on your fleet. Global Positioning System - High Performance GPS Products & Systems for Surveying, (GIS) Mapping, Precision Agriculture Machine Guidance, Port Automation, Mining and more! Fleet Tracking - Live 10 Second Updates, $29.95 Per Month - Protect your assets, monitor your drivers. Our GPS tracking and management solutions are powerful and affordable.

GPS Resource Library   This is a page of links containing information about the Global Positioning System (GPS) and handheld GPS units. Global Positioning System Overview An overview complete with graphs and photos. GPS Tutorial An easy-to-follow tutorial from Trimble Navigation Limited. The Global Positioning System A short history of navigation, from Columbus to GPS. The Global Positioning System: The Role of Atomic Clocks An article from The National Academies.