What Exactly is GPS?

GPS devices are here to stay. We see them everywhere, and they have shown their usefulness in all kinds of situations. But what exactly is GPS and how does it work?

GPS stands for Global Positioning System and it has been described as the only fully functional Global Navigation Satellite System. Other systems are currently (2008) in the process of development by Russia, Europe, China, and India. It consists of a set of satellites in medium orbit around the Earth, transmitting a precise microwave signal, that allows receivers to find out their exact location on the Earth's surface. The system was developed by the US Department of Defense.

The precise way in which these devices work is quite technical, but essentially the GPS receiver needs to be picking up a signal from at least three satellites. For this reason, there have to be about 24 or more satellites in the system, to ensure that more than three are "visible" in the sky to the receiver at any given time. By measuring the amount of time it has taken each signal to reach it from the transmitter, the receiver is able to calculate its distance from the satellite.

Theoretically three satellite signals are enough, because there are three dimensions of space, north-south, east-west, and up-down. But in practice a fourth reading is needed, in order to check the time variable against the other three readings. In almost every situation, there are at least four satellites visible, enabling the system to give accurate readings.

The three-dimensional coordinates are then converted into latitude-longitude or map references so that they can easily be interpreted by the user.

Robert Paterson writes for the blog "GPS Tracking" with advice, help, tips, ideas, information. Read more at http://phe-gps.blogspot.com/ and please feel free to leave a comment there.



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