Introduction to GPS technology

GPS satellites circle the earth twice a day in a very precise orbit and transmits signal information to earth. There are 24 satellites that make up the GPS space segment that are orbiting the earth at approximately 19,000 kilometres above us. They are constantly moving, making two complete orbits in less than 24 hours. These satellites are travelling at speeds of roughly 11,000 kilometres per hour. GPS receivers take this information and use triangulation to calculate the user's exact location. The GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map. A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position and track movement. With four or more satellites in view, the receiver can determine the user's 3D position (latitude, longitude and altitude). Once the user's position has been determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance and distance to destination.