Flytec 6030 * - Manual (Page 50)

Flytec 6030-GPS
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9.4.2 Accuracy of GPS Altitude
A good explanation of all effects on the GPS Altitude accuracy is found on the following link
http://www.kowoma.de/en/gps/errors.htm
First of all the word accuracy has to be defined: On the website above you can read: “The
declaration of the accuracy by Garmin GPS receivers often leads to confusion. What does it
mean if the receiver states an accuracy of 4 m? This readout refers to the so-called 50 %
CEP (Circular Error Probable). This means that 50 % of all measurements are within a radius
of 4 m. On the other hand, 50 % of all measured positions are outside of this radius.
Furthermore, 95 % of all measured positions are within a circle of twice this radius and 98.9
% of all positions are within a circle of 2.55 the radius. In the given example, nearly all
positions are within circle with a radius of 10 m. The determined position is in the worst case
accurate to 10 m. “
The position is derived from a triangulation. The GPS receiver measures the time of the
signals and calculates the distance. You can find a good explanation of the involved
calculations on Wikipedia.
For a 3D position it is necessary to see 4 satellites. The fourth satellite is needed for the
calculation of the time.
Earth radius
=6360km
Satellite orbit radius
=26560km
90°
Best Accuracy is achieved if the angle
between two satellites is 90°. The
triangle between your position and the
two satellites has then the biggest
possible area. The DOP is equal to
inverse value of this area.
4. satellite for time
synchronisation