Global Positioning System

• The GPS consists of a network, or constellation, of 24 active satellites, which circle the earth in a very precise orbit. The system was originally developed by the U.S. Air Force in the 1970s, but the satellites are now available for civilian use worldwide. The satellites transmit signal information to Earth and this information is used by GPS receivers on the ground to determine their precise geographical position. A GPS receiver must be able to "see" at least four satellites to calculate latitude, longitude and altitude, but the more signals it receives the higher the accuracy of the calculation. Modern global tracking devices can calculate position down to a matter of feet.
  
  

Transmitting Signals

• The important point to note is that a GPS receiver is just a receiver. It does not transmit signals to the GPS satellites or anywhere else, so a global tracking device must use another technology to transmit signals to a remote location. Global tracking devices typically include a cellular phone modem and they transmit signals over a cellular phone network so that they can be viewed, usually in real time, by the person what wants to know the location of the tracking device.
  
  

Active and Passive Tracking Devices

• Global tracking devices that transmit signals in, or near, real time are known as active tracking devices. If cellular network coverage is unavailable, they store location information until coverage resumes. This type of tracking device is used in situations where a fast response is required, such as tracking criminal offenders. Alternatively, so-called passive global tracking devices store location information and only transfer it to a monitoring center at periodic intervals.
  
  

Applications

• Global tracking devices vary in type, size and ability, but they have become increasingly commonplace and accurate in recent years. Some companies equip their vehicles with global tracking devices so that their location can be determined in the event of an accident or theft; even pet collars are fitted with global tracking devices to enable owners to find lost pets.