GPS is the acronym for the Global Positioning System. It is a planet-wide satellite navigation and positioning system with applications ranging from in-car “SatNav”, guiding combine harvesters and airliners, positioning oil rigs and weapons guidance systems.
Land Surveyors use it as a tool for precise positioning and also general surveying and mapping methods.
The system is a three dimensional measurement system which uses hand held and more precise survey instruments to receive radio signals from orbiting satellites to determine their terrestrial (surface) position.
GPS was developed by the United States Department of Defense and is managed by the United States Air Force 50th Space Wing located at Schriever Air Force Base near Colorado Springs, Colorado. Since it became operational in 1995 it has been the only fully functional satellite system (GNSS) in the world consisting of a constellation of between 24 and 32 orbiting satellites- allowing for life expectancy and depending on how many are working at the time.
The US also retains the royal veto in switching off some of the signals when they feel like it (selective availability) in order to prevent unscrupulous people from using the guidance system against them. Fortunately they have promised that they won’t do it anymore!
With the rise in tourist applications of GPS and the desire of other continents not to be completely reliant upon US satellites, other positioning systems are developing, though not fully functioning yet. For example the European Galileo, Russian Glonass and recently the Chinese regional Beidou navigation system is being expanded into the Compass Global System. These are now all known by the generic term Global Satellite Navigation Systems (GNSS).