# How gps works?

Gps means global positioning system. A small gadget having gps receiver tells you about your current location or where you are standing on the earth at that particular moment. Earlier people used landmarks, maps etc to save themselves from getting lost but now gps is the easiest way to know about your exact position.

Generally when we talk about gps people take it as a gps receiver but in actual it is a group of 24 satellites orbiting around our planet with five stations on the ground which keeps the satellite in a proper orbit with an altitude of 10900 miles. These satellites orbit the earth twice a day. They move in such a way that on any part of the earth there are at least four satellites that can be approached. This system was developed and used by U.S. for military navigation system. The idea was conceived in 1970 by the department of defense. It was used to know the exact positioning of missiles and submarines because the earlier methods were not much accurate and they were very much influenced by atmospheric conditions, enemy jamming etc. but later on in 1980â€™s this was open for all the civilians and common people.

Work of gps receiver is to find four or more satellites and calculate its distance from each of them to trace its own position. It works on a principle of trilateration which means to know the location of particular thing on the earth through geometry of triangle.

WORKING OF GPS
First of all it works outdoor and can perform well where it has clear visibility of sky. That is why it cannot work properly in the congested areas having tall buildings and forests.
Satellites in the network send signals of time and data about their location to the receiver on the earth. These signals travel at the speed of light. Signals from different satellites are received at different times because some satellites are near and others are farther. Distance of these satellites can be calculated through the difference in time for the signals to reach the receiver. After calculating the distance of minimum of four gps satellites the receiver tells about its three-dimensional location. Receiver knows that it is somewhere on the surface of an imagined sphere centered at a satellite. Then it determines the size of all the spheres of different satellites. So finally receiver determines its position at the intersecting points of these spheres.

When we calculate the distance from one satellite we come to know that we are on the surface of an imaginary sphere which has the same radius as the distance to the satellite radius. When the distance from the other satellite is calculated we come to know that our location is somewhere on the intersecting point of these two spheres which is two-dimensional location. After the third and fourth measurement of spheres the exact location is known which is three-dimensional.

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