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RTK Mapping 8
Note – You cannot derive a Local Site Calibration using the Asset
Surveyor software.
For best results, assuming the control is free of errors, local control
points should be evenly distributed over the data collection area as
well as extending beyond the perimeter of the site. A minimum of
three known points is recommended for a horizontal adjustment, while
a minimum of four known points is recommended for a vertical
adjustment.
A local site is the result of plane and height adjustments. The plane
adjustment consists of a rotation, translation, and scale change of the
mapping plane. The height adjustment defines a plane that is inclined
relative to the mapping plane. A mapping plane is an underlying
coordinate system that already has defined datum and map projection
parameters.
Creating a local site is a simple way to compute the parameters
(rotation, translation, and scale) associated with a plane adjustment for
a localized area, or site. Vectors define the relative movements of
positions for known coordinates. A least squares adjustment is then
applied to the vectors to derive a best fit solution for the parameters of
the plane adjustment.
Some important points to remember when creating a local site are:
A local site is created from a specific coordinate system and
zone; it is linked permanently to that zone. Make sure that the
current coordinate system and zone are the same as that of your
existing database.
A local site can only be created in terms of a cartesian
coordinate system (that is, not from a latitude/longitude
projection). This is because a local site is defined in linear units,
such as meters, as opposed to non-linear units, such as degrees.
TSC1 Asset Surveyor Operation Manual 195