What is Automotive navigation system?
[[File:ConstellationGPS.gif|thumb|240px|right|The earth with the [[GPS]]-[[satellite]]s turning around it. The number of visible satellites is always changing. That is given here in '''blue''' for 45° North latitude at any moment during the earth's rotation.]] '''Car navigation''' allows an [[automobile]] driver to see where he or she is on a [[map]] at any given time. Automobile [[navigation]] can rely on [[GPS]] (Global Positioning System), or it can be [[DVD]]- or data-based. GPS-bsed navigation uses radio signals from special [[Satellite (artificial)|satellites]] that send their position and the time of [[Transmission (mechanics)|transmission]]. The GPS receiver catches the signal and calculates the time. The GPS can then calculate the distance from the satellite with the well-known [[Speed of light|radio signal speed]]. ==Satellites== When driving a car with such a GPS receiver, the driver may receive information from a satellite which is above for instance [[Dover]] in the south and another one which is above [[Perth, Perth and Kinross|Perth]] in the north. Then the GPS receiver knows precisely how far it is from Dover and how far it is from Perth. With that ''two'' possible positions of the car at the flat land are precisely determined. To know which one of those positions is the right place, the GPS receiver needs a third satellite, for instance above [[Land's End]] in the west. With that information, the GPS receiver can also determine elevation. With three satellites in fact there is still a third possible point, but that is twice as high as the satellites above the earth's surface and does not need to be reckoned with in car travel. But the GPS receiver still needs a fourth satellite, because the GPS receiver needs to know the time very precisely. In between it knows your car position, so that it can calculate the distance from that satellite. Then it knows the time of reception, because that is the time of transmission plus the travel time of the signal. == The GPS receiver == [[Image:TomTomOne.j