Abbreviation for Global Positioning System. A satellite based global positioning system. The network of 24 satellites (plus 4 reserve satellites) currently operating, developed by the American army and made available to civilians. GPS can determine the geographical coordinates of any point on the globe. It can be accurate to 1 metre. GPS is used with a map to find bearings and position in rambling, sailing, trekking etc.
How GPS works
The working principle of GPS is based on measuring the distance of a receiver from several satellites (the satellites are distributed in such a way that between 4 and 8 of them are always visible). Each satellite transmits a signal which is picked up on Earth by a receiver, thus allowing accurate measurement of the distance between the transmitter and the receiver from the transit time.
On receiving the signals from four satellites (three to obtain the point of intersection of three spheres and a fourth for time synchronisation), the mobile receiver can calculate the geographical position by triangulation.
Until 2000, GPS accuracy was deliberately downgraded by the American army and today is of the order of one metre, but it depends on the equipment used and the number of visible satellites.
The association of a GPS receiver and a map application is used to provide an effective road navigation system, with display of a map and audio directions by vocal synthesis. This comes in several forms: on-board vehicle systems, independent box with integrated receiver, personal assistant or smart phone associated with a GPS receiver.
GPS is a passive system that receives signals from satellites and deduces a position from them. © DR