Furuno GD-280, Operator'S Manual

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10-1
10. GPS, DGPS SETTINGS
10.1 GPS Receiver (built-in GPS receiver only)
10.1.1 GPS overview
GPS is an acronym meaning Global Positioning System. GPS (sometimes referred to as
NAVSTAR) is a highly precise satellite navigation system developed by the U.S. Department of
Defense.
A constellation of satellites (approximately four satellites each in six orbital paths) emplaced in
nearly 20,000-kilometer high 12-hour circular orbits provides highly precise, continuous,
worldwide, all-weather position plus time and velocity information to GPS receiver-equipped
vehicles, vessels and aircraft.
How the GPS receiver calculates position
The GPS receiver's position is continuously fixed by receiving 3 (or 4) satellites in line-of-sight of
the GPS receiver. The basic steps in position fixing are as below.
•
GPS satellites continually transmit their own precise orbital data called ephemeris. The GPS
receiver computes satellites' position by this data.
•
The GPS receiver measures very accurate distance to the satellites.
•
Satellite locations and their distances from the GPS receiver are known. The GPS receiver
fixes its own position by triangulation.