How it works
The global
positioning system (GPS) consists of 24 operational satellites (with
several spares) orbiting the earth at an altitude of approximately
11,000 miles.
The satellites orbit
the earth twice per day in a pattern which ensures that at least 4
satellites can be viewed from the earth at any position any time of
the day. Typically however between 5 and 7 satellites may be in
view.
These satellites
broadcast signals which are analysed by GPS receivers on the earth.
The signals carry information such as the satellite identifier, it's
position, and an extremely accurate date and time (derived from an
on board atomic clock).
GPS receivers on the
ground use the signal from at least 4 satellites to determine their
own position with an accuracy of around 10 to 20 metres.
The GPS
receiver also contains a GSM GPRS device inside (much like that
found inside a mobile phone). This allows the receiver to transmit
its information from the receiver back to the host server in real
time via the internet.
The GPS receiver
also calculates a variety of fleet management information (speed,
heading, distance, idling,
driver
behavior) which is transmitted
along with the position information.
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