Leica Geosystems GPS Basics - Manual (Page 40)

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GPS Basics -1.0.0en Surveying with GPS
5.1.1 Static Surveys
This was the first method to be devel-
oped for GPS surveying. It can be used
for measuring long baselines (usually
20km (16 miles) and over).
One receiver is placed on a point whose
coordinates are known accurately in
WGS84. This is known as the Reference
Receiver. The other receiver is placed on
the other end of the baseline and is
known as the Rover.
Data is then recorded at both stations
simultaneously. It is important that data
is being recorded at the same rate at
each station. The data collection rate
may be typically set to 15, 30 or 60
seconds.
The receivers have to collect data for a
certain length of time. This time is
influenced by the length of the line, the
number of satellites observed and the
satellite geometry (dilution of precision
or DOP). As a rule of thumb, the observa-
tion time is a minimum of 1 hour for a
20km line with 5 satellites and a
prevailing GDOP of 8. Longer lines
require longer observation times.
Once enough data has been collected,
the receivers can be switched off. The
Rover can then be moved to the next
baseline and measurement can once
again commence.
It is very important to introduce redun-
dancy into the network that is being
measured. This involves measuring
points at least twice and creates safety
checks against problems that would
otherwise go undetected.
A great increase in productivity can be
realized with the addition of an extra
Rover receiver. Good coordination is
required between the survey crews in
order to maximize the potential of having
three receivers. An example is given on
the next page.