GNSS (Global Navigation Satellite System) is a satellite system that is used to pinpoint the geographic location of a user's receiver anywhere in the world. Two GNSS systems are currently in operation: the United States' Global Positioning System (GPS) and the Russian Federation's Global Orbiting Navigation Satellite System (GLONASS).
Both of these employ a constellation of orbiting satellites working in conjunction with a network of ground stations. The accuracy and integrity of GNSS can be improved by augmenting it with correction data to minimise the system errors. Such augmentation is usually based upon a concept referred to as differential in which case GNSS becomes DGNSS (differential global navigation satellite system).
In future, two additional systems will be added to the GNSS family with the introduction of the European Galileo system and the Chinese COMPASS (CNSS) system.