Our ancestors used to work extremely hard to protect themselves from getting lost in this mysterious world. They used to erect monumental landmarks, study conventional land maps and of course they used to mark the stars in the night sky.

But today it is very easy to know one's position. You just only have to get a pocket-sized gadget that will make you know your exact position on this earth at any given moment. The system of knowing one's exact position on this earth is known as 'Global Positioning System'. If anyone has a Global Positioning System (GPS) receiver, and if the sky remains clear, then no way can he get lost on this earth.

Of note is that this pocket-sized gadget, the Global Positioning System receiver, is quite expensive and it also involves a fair amount of technical ingenuity.

GPS is specially a Satellite Navigation System that helps in tracking our exact location with the help of satellites. The Global Positioning System is mainly funded and controlled by the U.S Department of Defense (DOD). The system was primarily designed for the operation of U. S. military. But there are also many civil users of GPS across the globe. The Global Positioning System provides some special satellite signals which are then processed in the GPS receiver. These GPS receiver's not only track the exact location, but can also compute velocity and time.

The positions can even be computed in three dimensional views with the help of four GPS satellite signals. The Space Segment of the Global Positioning System consists of the GPS satellites. These satellites send radio signals from space which are received by the GPS receiver.

There are more than 24 operational and 3 extras (in case one fails) GPS satellites that moves round the Earth every 12 hours.

The control of the Global Positioning System consists of different tracking stations that are located across the world. These monitoring stations help in tracking signals from those Space Vehicles which are continuously orbiting the earth. The Space Vehicles transmit microwave carrier signals. The users of the Global Positioning System have GPS receivers that convert the satellite signals which estimate position, velocity and time. Four satellites are required to track the three dimensional location and time. The primary function of Global Positioning System is the navigation in three dimensions. The Navigation receivers are used for aircraft, ships, and ground vehicles and sometimes for personal use as well.

With GPS receivers, precise positioning of any location can be done. The Global Positioning system is based on a simple mathematical calculation that operates through a process called Trilateration. In order to make the simple mathematical calculation the GPS receiver should know two things.

++ One is the location of the place to be traced by at least three satellites.

++ Secondly, is the distance between the where the receiver is located and each of those Space Vehicles.

All units have multiple receivers, and can pick up signals from several GPS satellites at a same time. These radio waves are electromagnetic energy that travels at the speed of light.

The civil users across the world are allowed to use the Standard Positioning Service without any kind of charge or restrictions.

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