09/25/02
GPS_field_guide
8:19 A9/P9
6
3. Repeats the operation mentioned under point 2 with a third satellite. In our example
the receiver finds out that it is 20,000 km from the third satellite which narrows its
position down even further, to the two points (Figure 5 point b) where the 20,000 km
sphere cuts through the circle reported on Figure 4 (corresponding to the intersection
of the first two spheres).
Figure 5
- Potential locations of the GPS receiver with 3 satellites signals (
b
)
Most of the time one of these two points is absurd and is rejected by the receiver that
is then able to give the exact location. In some cases, a fourth satellite is necessary to
know which of the two points is the correct one. In any case, a configuration with 4
satellites is better in order to increase the accuracy and/or reduce the sources of error.
Summary of Contents for GPS
Page 1: ...GPS Field guide WHO 2002...