Ever wondered how GPS works?

Beginners guide to GPS

Claire Mcentee

July 16, 2009 - 12:01AM

GPS stands for Global Positioning System and refers to a satellite-based navigational system developed by the United States Department of Defence and operated by the US Air Force.

Officially called NAVSTAR GPS, it was made it available for civilian use in the 1990s.

GPS technology has multiple applications but is perhaps best known for its use in car navigation units, such as those sold by TomTom and Navman.

The units use GPS to help drivers navigate unfamiliar roads or find certain locations and can also tell them how fast they're driving and warn of speed cameras ahead.

Most new smartphones have GPS receivers and with the right software can be used to navigate and even find the location of others - with their permission.

Google's Latitude software and Yahoo!'s FireEagle software use GPS to track people's cellphones and display their location on online maps such as Google Maps.

Users need to download the software to a GPS phone and must ask permission before they can view a friend's location.

Star Droid is another GPS software product developed by Google for mobile phones.

Users with GPS phones can point the phone's camera to the night-sky and read the names of the stars and planets captured through its viewfinder. The software uses GPS to identify the location of a person and compares it with maps of space.

How it works

Twenty-four satellites circle the Earth twice a day in precise orbits, transmitting signals that are picked up by GPS receivers - such as those in car navigation units.

The receivers use signals from different satellites to determine how far away the satellites are and then calculate where they are on earth. GPS receivers must lock on to the signal of at least two satellites to pinpoint someone's latitude and longitude, and four or more to determine someone's latitude, longitude and altitude.

Once a GPS unit knows where you are, it can then calculate other factors such as your speed and direction.

In GPS devices, location information is commonly used with mapping software to give directions.

Most GPS receivers are accurate but atmospheric conditions and things such as tall buildings and tunnels can cause inaccuracies or prevent the satellite signal reaching the receiver.

Russia, China and the European Union are launching satellites to create their own satellite navigation systems.