Global Navigation Satellite Systems (GNSS) provide autonomous geo-spatial positioning with global coverage. The orbiting Satellites sends out signals to ground receivers, which accurate determine the satellite location in longitude, latitude and altitude and the receivers calculate the current local time to high precision. NAVSTAR the U.S. Global Positioning System (GPS) and GLONASS the Russian Positioning System are active parts of the GNSS. The European System GALILEO and the China System COMPASS are in process to contribute the Global Navigation Satellite System. Each system have their own satellite constellation.
International GNSS Service (IGS).