90 MPC User Manual Rev 0D
Appendix B GPS Overview
Figure 83: Single-Point Averaging
*This graph represents typical results using position averaging.
This function is useful for obtaining the WGS84 position of a point to a reasonable accuracy without
having to implement differential GPS. It is interesting to note that even a six h our occupati on can
improve single-point GPS accuracy from over fifty meters to better than five meters. This improved
accuracy is primarily due to the reductions of the multipath and selective availability errors in the GPS
signal.
Again, it is necessary to keep in mind that the resulting standard deviations of the position averaging
can vary quite a bit, especially over relatively short averaging times. To illustrate, the position
averaging function was run for a period of one hour at three different times during the day. The
resulting standard deviation in latitude varied from 4.7 to 7.0 meters. Simi larl y, the variation in
longitude and height were 4.9 to 6.7 meters and 10.9 to 12.5 meters respectively. This degree of
variation is common for averaging perio ds of less than 12 hours due to changes in the satellite
constellation. The graph, however, should at least provide some indication of the accuracy one may
expect from single-point position averaging.
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Tim e (hours)
Standard Devi ati o n (meters)
Latitude Longtitude Height