The Global Positioning System (GPS), a version of GNSS, originally Navstar GPS, is a satellite-based radio-navigation system owned by the United States government and operated by the United States Air Force. It is a global navigation satellite system that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites.

Obstacles such as mountains and buildings block the relatively weak GPS signals.