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GPS what it is, and how it works Most people, if they ever think about their Sat-Nav system, will usually be thinking about their boat, or car's Sat-Nav system. However this system in their vehicle, is in fact only the Global Positioning Systems receiver. This is the device which receives, and translates the incoming satellite signal into your actual geographical position. How GPS systems calculate your position. GPS is shorthand for Global Positioning System. At any one time there are at least 24 satellites in orbit around the earth. At any one time, any location will be covered by, and receiving signals from at least four satellites. Initially the GPS network was developed by the American military to enable accurate troop deployment. However, since the mid 1990's it was made available to all - at least anyone with a GPS receiver that is. Since the position of each satellite is known, and monitored from earth, and the GPS receivers are pre-programmed with this information, allowing your GPS system to translate this into co-ordinates of your position. Each of the orbiting satellites go around the earth twice a day. All of the satellites are linked to each other, and they each synchronously transmit a signal with their exact location, and the time at which the signal was transmitted. Due to their exact orbits, the satellites, will all be at different distances from your GPS system. As stated this could be your boats GPS, or chart plotter system, or car sat nav. Thus because of the slight difference in position and range, the signals won't all get to your system at exactly the same instant. So when the signals arrive at your GPS device, it will hear each discrete signal, and using the tiny delay between each signal, will be able to work out the position of each of the satellites (this process is called triangulation, and having this information, it can calculate your position. GPS system limitations. The first limiting factor for GPS receivers, is that they must receive a message from a minimum of 4 satellites. This is to ensure an accurate position to be worked out. A clear view of the sky is necessary to ensure that the signals are able to be received. Weather can occasionally affect the signal quality as well. Sat-Nav system manufacturers will therefore usually advise placing your Sat-Nav, or it's Ariel, with an clear view of the sky whenever this is possible to try to ensure the best signal quality. Accuracy of your GPS systems? The accuracy claimed by various GPS system makers will vary, Some will quote best levels, whilst others will settle on a more general figure. Most GPS units however are accurate to within a few meters usually, and are accurate enough to do their job. Another thing to remember with GPS units is the satellite acquisition time, again the times quoted by different manufacturers will differ, and the "cold" acquisition times, that is the time from switching on you GPS unit can sometimes be several minutes. It may be even longer, given any of the adverse variables mentioned above. A word of cation when using GPS systems, do not blindly follow their directions, especially if you can see that it will lead you into a dangerous situation. They are meant as an aid to navigation, and not as the last word. You as the user are ultimately responsible for using your GPS safely.
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GPS, Global Positioning System, Navigation, sat nav,
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