Nowadays GPS (Global Positioning System) is a well known reality that has already become a standard of life for many people. The aim of this arrangement is the defining of the velocity and situation of the objects. It can define the object at any place on Earth, even in polar territories and in space to 100 kilometers above Earth in any weather conditions. The United States Department of Defense has worked out and accomplished NAVSTAR GPS.
The situation is identified by the principle of measuring the distance from the spot with the fixed coordinates to an object. The sending satellite spreads the signal to a GPS antenna and the delay time is calculated to define the distance between the receiver and transmitter. You can see that GPS receiver has to know the distance to 3 satellites and the time of the GPS system to identify 3-dimensional coordinates. And to define a receiver's coordinates and altitude it has to use minimum 4 transmitters' signals. The direction of the satellites from Earth is realized in the control station that is situated in Schriever base, Colorado.
GPS receivers are frequently used today by average people, sailors, rescuers and the police for position and speed detection of different objects. If you need handheld GPS systems you can buy it almost anywhere nowadays. It is also built in the most personal computers, cellular phones and onboarders. With a GPS receiver a user can indicate his geographical coordinates at the definite period of time. The maximum accuracy is from 3 to 5 meters and with the correction signal from Earth it is to 1 millimeter.
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