GPS Reciever

Now as days GPS receivers are very cheap. You can easily get one with a serial interface for not more than 100$. These devices work anywhere on the earth. The GPS system is made up of a satellite constellation of at least 24 satellites in an intermediate circular orbit (ICO), in 6 orbital planes. Each satellite circles the Earth twice every day at an altitude of 20,200 kilometers (12,600 miles). The satellites carry atomic clocks and constantly broadcast the precise time according to their own clock, along with administrative information including the orbital elements of their own motion, as determined by a set of ground-based observatories. The ground stations around the world monitor the flight paths of the GPS satellites, synchronizing the satellites' onboard atomic clocks, and uploading data for transmission by the satellites. A GPS receiver compares time signal transmissions from four or more satellites to calculate the precise time and its current position (latitude, longitude, and elevation), using trilateration. The receiver computes the distance to each of the four satellites from the difference between local time and the time the satellite signals were sent (this distance is called a pseudorange). It then decodes the satellites’ locations from their radio signals and an internal database.

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