A
satellite navigation or
satnav system is a system of
satellites that provide autonomous geo-spatial positioning with global coverage. It allows small
electronic receivers to determine their location (
longitude,
latitude, and
altitude/
elevation) to high precision (within a few metres) using
time signals transmitted along a
line of sight by
radio from
satellites. The signals also allow the electronic receivers to calculate the current local time to high precision, which allows time synchronisation. A satellite navigation system with global coverage may be termed a
global navigation satellite system (
GNSS).