The basis of GPS (Global Positionning System) is in receipt of at least four radio signals from as many satellites which are very accurately known orbital position with respect tothe ground, simultaneously very well known While such signals have been slow to take the path between the satellite and receiver.
Knowing the position of satellites, the propagation speed of signalsand the time taken to reach the receiver, you can set the receiver's position on Earth by triangulation calculations.
Currently the GPS system has 3 levels:
Spatial level: 24 Navstar satellitespermanently emitting signals with the following data:
• orbital position
• exact time signal emissions
• the calendar, ie the position of all other GPS satellites.
These data are transmitted inthe form of electromagnetic waves with microwave frequency between 1.6 and 1.2 GHz
To complement the Navstar network, managed by the U.S. government, the European Union promotes the Galileo projectwill be operational from 2008.
The Global Positioning System (GPS) is a tracking system, designed by the Department of
United States Defense for military purposes to provideprecise estimates of position,
speed and time, operating since 1995 using together a network of computers and a constellation of 24
satellites to determine by triangulation, altitude, latitude andlongitude of any object on the surface
Earth  - .
In civil and security grounds only allows the use of a subset gradient
GPS signals. However, the civilian community has found ways to obtainan excellent precision
location through so-called differential techniques. Because of them have civilian applications
experienced tremendous growth and currently there are over 70 manufacturers ofGPS receivers.
A similar navigation system called GLONASS (Global Navigation Satellite System) was developed in the
former Soviet Union. The system is also designed for military purposes,...
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