The is a satellite navigation system. GPS is funded by and controlled by the U. S. Department of Defense (DOD). While there are many thousands of civil users of GPS world-wide, the system was designed for and is operated by the U. S. military.
It provides specially coded satellite signals that can be processed in a GPS receiver, enabling the receiver to compute position, velocity and time.
Four GPS satellite signals are used to compute positions in three dimensions and the time offset in the receiver clock.
Based on a constellation of 24 satellites in very high orbit, the system avoids problems encountered by land-based systems and provides accurate positions anywhere in the world, 24 hours a day. GPS receivers are becoming small enough and cheap enough to be used cost-effectively in a wide variety of applications, ranging from electronic navigation for cars to landing aircraft in zero-visibility conditions. In geography, perhaps the greatest potential of GPS is as a tool for capturing both positional and attributes data for use in geographic information systems (GIS). Global Positioning Systems |
