How Sat Nav Works
Sat Nav, also known as Sat-Nav, GPS-Nav and Satellite
Navigation uses GPS, (Global Positioning System) and some complex software with
maps to allow the user of the Sat Nav, (Satellite Navigation), to know exactly
where the user is, in which direction the user is travelling, at what speed, and
for how long. Using complex maps and this geographical pin-pointing, Sat Nav is
a globally recognised tool used by millions of users
across the world.
GPS, (Global Positioning System), works on a triangulation method. Triangulation is the method of determining a location of a map by using three or more points through which lines of known directions are drawn. The intersection of these lines is the desired location. Triangulation can be used for working out distance and/or angles. Ideally, 4 satellites are required to offer an exact position. 3 satellites will work, but 4 are proven to be better as the extra satellite will assist in error checking the other satellites. To fully triangulate, a GPS (Global Positioning System), receiver measures the distance from the satellites, (the distance is worked out by measuring how long a radio signal takes to reach the Satellite Navigation device from that satellite). To correctly measure this signal, a comparison of the time the signal from the satellite was sent against when it was received. This is multiplied by the speed of light, and the distance is calculated. All GPS (Global Positioning System), satellites are fitted with atomic clocks which means their time is permanently accurate, (too within 1 second per 300,000 years). It is this accuracy which is key to ensuring that the timing of both the GPS (Global Positioning System) and the satellite are synchronised.
If a GPS (Global Positioning System) receiver is not
totally accurate, it will not matter greatly, as they can calculate the errors
and correct them. Along with the distance, the exact position of the satellite
in space is required. To use the satellites as references for range
measurements, their exact position is essential. Due to their high orbits,
(between 10,600 miles and 12,625 miles above the earths surface), they very rarely go off course; therefore they can be almost totally relied
upon. The US department of defence is able to transmit
information to these satellites correcting orbits and sending appropriate
geographical information if necessary. Corrections for the delays in the signal
being received must also be calculated into. There are various layers for the
signals to pass, such as the ionosphere and the atmosphere. These can cause
delays in the GPS (Global Positioning System), which means positional errors.
Most of these can be factored out using mathematics.
