Oxford Technical Solutions
36
Figure 11.
Averaging to a different position example
The problem of averaging to a different position happens each time that the GPS-Base goes
through its averaging process. There is nothing magical about the GPS-Base that allows it to
get its own position accurate to 2 cm or better. It is subject to the same errors that all GNSS
receivers have and can only average its position to about 1.8 m CEP.
If the user is prepared to wait a long time (typically more than 24 hours) then GNSS is able to
improve the accuracy of the base station antenna so it is accurate to 2 cm or better. However,
since the timescale for this is long it is not usually practical, except for permanent
installations. (Even when you have a permanent installation it is not required since all it does
is allows you to relate your measurements to a surveyor's measurements and this is rarely
required).
To overcome the problem of averaging, the save/restore feature of the GPS-Base should be
used. When using the Save/Restore feature the GPS-Base will save the position where it last
averaged and then use this next time (instead of averaging again). This way the error is the
same each time and the repeatability is perfect. You must remember to put the antenna in the
same location each time, accurate to 1 cm or better, when using the Save/Restore feature.
