v5.20 - Classic DocuShare Home - Trimble

8 RTK Mapping
C
A local site created in the GPS Pathfinder Office software must
be transferred to your datalogger for use in the field. For more
information on transferring a local site, refer to the GPS
Pathfinder Office documentation.
Local sites can be created and edited using the Coordinate
System Manager. For more information about creating and
editing sites, refer to the GPS Pathfinder Office documentation.
Geoid models
The geoid, as mentioned above, is a surface of constant gravitational
potential which approximates mean sea level. A geoid model (also
called a geoid grid file) is a table of separations between the geoid and
the ellipsoid. Heights of GPS positions are computed relative to the
WGS-84 ellipsoid. Using a geoid model, the separation between the
geoid and the ellipsoid is calculated and added to the ellipsoid height,
to compute the elevation of the point above the geoid, often referred to
as height above mean sea level (MSL).
You can incorporate a geoid model into your local site as a Height
Adjustment. The geoid-ellipsoid separations are taken from the geoid
file you choose, then used to display elevations, which are shown on
the screen.
The benefits of this function are that you can display elevations
(which are only as accurate as your geoid model) without having to
calibrate on elevation benchmarks. This is very useful when there is
no local control or benchmarks, as it enables you to work on the
ground rather than on the ellipsoid.
Remember elevations that are derived from geoid models are only as
accurate as the geoid model used to determine them.
Warning – The Asset Surveyor software references a geoid model with a
grid separation of 10 degrees x 10 degrees for standard derivations of
elevation above mean sea level, which is too coarse for RTK operations.
Use a local site calibration if absolute accuracy is desired.
196 TSC1 Asset Surveyor Operation Manual