satnav uses a system of satellites. the system gives exact positioning. it allows small electronic receivers to find their position (longitude, latitude, and altitude/elevation). the position is given within a few metres using time signals transmitted along a straight line (line of sight) by radio from satellites. the signals also allow the receivers to calculate the current local time to high precision. a satellite navigation system with global coverage may be called a global navigation satellite system (gnss). global positioning system is the biggest and most used gnss. glonass, owned by russia, is the second biggest. china, india, and the european union are working on similar systems of their own.