GPS - How it works

GPS (Global Positioning System) is based on a network of more than 24 satellites travelling around the world every 12 hours that sends out exact information on time and position.

The GPS system was originally developed for military use by the US Department of Defence, but a less precise form of the service became available free of charge to civilian users around the globe.

The basic civilian service is able to locate a GPS receiver with an accuracy of 10 meters. However, various augmentation methods can be used to determine the geographical location within 1 cm.

The GPS receiver calculates its position from the information it receives from the surrounding satellites. 3 satellites are needed to determine the GPSs location (the intersection of three spheres gives one unique location on the earth surface - see picture below). Information from a 4th satellite is used to determine the direction of the GPS receiver.

Detecting geographical location on the earth by the use of 3 satellites

The satellites follow 6 different orbits and each satellite repeat the same track and configuration over any point approximately every 24 hours. This makes five to eight (or sometimes more) satellites visible anywhere on the Earth at any time.

GPS receiver

There are many different types of GPS receivers in the market and they have become less expensive and smaller in recent years. The GPS receivers are now small enough to be integrated into mobile phones.