•
are tables of correction values to convert coordinates directly from
WGS 1984 to local grid without the need of transformation parameters.
•
take the distortions of the mapping system into account.
•
are an addition to an already defined coordinate system.
Types of CSCS models
The correction values of a CSCS model can be applied at different stages in the
coordinate conversion process. Depending on this stage, a CSCS model works
differently. Three types of CSCS models are supported. Their conversion proc-
ess is as explained in the following table. Any suitable geoid model can be
combined with a geodetic CSCS model.
Type
Description
Grid
1
Determination of preliminary grid coordinates by
applying the specified transformation, ellipsoid and
map projection.
2
Determination of the final local grid coordinates by
applying a shift in Easting and Northing interpolated in
the grid file of the CSCS model.
Cartesian
1
Performing the specified transformation.
2
Determination of local cartesian coordinates by apply-
ing a 3D shift interpolated in the grid file of the CSCS
model.
3
Determination of the final local grid coordinates by
applying the specified local ellipsoid and map projec-
tion.
Geodetic
1
Determination of local geodetic coordinates by apply-
ing a correction in latitude and longitude interpolated
from the file of the CSCS model.
2 Determination of the final local grid coordinates by
applying the local map projection.
☞
Using a geodetic CSCS model excludes the use of a
transformation in a coordinate system.
Description
The
C
oordinate
Q
uality is
•
computed on the rover for code solutions and phase fixed solutions.
•
an indicator for the quality of the observations.
•
an indicator for the current satellite constellation.
•
an indicator for different environmental conditions.
•
derived such that there is at least a two third probability that the compu-
ted position deviates from the true position by less than the CQ value.
•
different from the standard deviation.
CQ versus standard deviation
The standard deviation as CQ would often be too optimistic, therefore the com-
putation of the CQ is not based on the basic standard deviation algorithms.
There is a 39.3% statistical probability in 2D, that the computed position devi-
Coordinate quality for
GS
Glossary
1041
