Then A moves to E and C moves to
8. The triangle BDE is measured.

The network ABCDE has to be After the required length of time, the
measured with three receivers. The receiver that was at E moves to D
coordinates of A are known in and B moves to C. The triangle ACD
WGS84. The receivers are placed on is measured.
A, B and C. GPS data is recorded for

The end result is the measured
Finally, B moves back to C and the network ABCDE. One point is mea-
line EC is measured. sured three times and every point has
been measured at least twice. This
provides redundancy. Any gross errors
will be highlighted and the offending
measurement can be removed.

2. Rapid static survey

In Rapid Static surveys, a Reference Point is chosen and one or more Rovers operate with respect to it.
Typically, Rapid Static is used for densifying existing networks, establishing control etc. When starting
work in an area where no GPS surveying has previously taken place, the first task is to observe a number
of points, whose coordinates are accurately known in the local system. This will enable a transformation to
be calculated and all hence, points measured with GPS in that area can be easily converted into the local
system. As discussed in section 4.5, at least 4 known points on the perimeter of the area of interest should
be observed. The transformation calculated will then be valid for the area enclosed by those points. The
Reference Receiver is usually set up at a known point and can be included in the calculations of the
transformation parameters. If no known point is available, it can be set up anywhere within the network.

The Rover receiver(s) then visit each of the known points. The length of time that the Rovers must observe
for at each point is related to the baseline length from the Reference and the GDOP.