Flytec 6030 * - Manual (Page 51)

Flytec 6030-GPS
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In case of a 3D position, best accuracy is achieved if the 3 satellites are 90° to each other. In
this case the volume of the pyramid is biggest. Again the DOP is equal to the inverse of this
volume.
For a good 2 D position on the earth surface it is best, if you have 2 satellites near the
horizon. The third satellite perpendicular above you, gives only a rough information of the
altitude, but for a good lat/long triangulation this is good enough.
The chance that you will find two satellites with 90° near the horizon and on above you, is
better than to find 3 satellites with 90° to each other directly above you.
Because the circumference area above the horizon is bigger than the area of the calotte
above, there is a bigger chance to have satellites in this area than above you. Additionally
the horizontal accuracy is better with satellites near the horizon. The GPS module will
therefore prefer satellites near the horizon instead of satellites horizontally above you. For
the horizontal position, the GPS receiver will calculate different satellite positions and make
an average of this positions every second to increase the accuracy.
To do the same with the vertical position, the receiver needs twice the calculation power. So
it is easier to calculate only one vertical position per second and to average the last few
positions.
That is the reason for the visible delay.
Time difference
satellite 1
45°
This circumference
area is bigger than
the calotte above
Calotte
Satellite 1
Satellite 2
Almost no Time
difference satellite 2
Position A Position B