Global Positioning System

Global Positioning System (GPS) is a space-base radio positioning, navigation, and time-transfer system for locating geographical location.
GPS system consists of 24 satellites that orbit the earth and there are 4 satellites in each orbit. These satellites are called NAVSTAR and orbit the earth twice a day in a precise orbit, sending information signals to the earth.
The system provides highly accurate position and velocity information, and precise time, on a continuous global basis, to an unlimited number of properly equipped users. The system is unaffected by weather, and provides a worldwide common grid reference system. The GPS concept is predicated upon accurate and continuous knowledge of the spatial position of each satellite in the system with respect to time and distance from a transmitting satellite to the user. The GPS receiver automatically selects appropriate signals from the satellites in view and translates these into three dimensional position, velocity, and time. System accuracy for civil users is normally 100 meters horizontally.