Leica Geosystems GPS Basics - Manual (Page 42)

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GPS Basics -1.0.0en Surveying with GPS
5.1.2 Rapid Static Surveys
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, establish-
ing 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 mea-
sured 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 avail-
able, 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.
The data is recorded and post-proc-
essed back at the office.
Checks should then be carried out to
ensure that no gross errors exist in the
measurements. This can done by
measuring the points again at a different
time of the day.
When working with two or more Rover
receivers, an alternative is to ensure that
all rovers operate at each occupied point
simultaneously. Thus allows data from
each station to be used as either
Reference or Rover during post-
processing and is the most efficient way
to work, but also the most difficult to
synchronise.
Another way to build in redundancy is to
set up two reference stations, and use
one rover to occupy the points as shown
in the lower example on the next page.