Leica GPS900 Series, Technical Reference Manual

Page: 188 / 287

Working with Determine Coord System GPS900 188
• One point: Heights are shifted to fit to the height control point.
• Two points: Average height shift between the two height control
points.
• Three points: Tilted plane through the three height control points
to approximate the local heights.
• More than three points: Best fitting average plane.
Advantage • Errors in height do not propagate into errors in position since the
height and position transformations are separated.
• If local heights have low accuracy or do not exist, a transforma-
tion of position can still be calculated and vice versa.
• The height points and position points do not have to be the same
points.
• No parameters of the local ellipsoid and map projection is
required.
• Parameters may be computed with a minimum of points. Care
should be taken when computing parameters using just one or
two local points as the parameters calculated are valid in the
vicinity of the points used for the transformation.
Disadvantage • Restriction in the area over which the transformation can be
applied. This is mainly due to the fact that there is no provision
for scale factor in the projection.
• The accuracy in height depends on the undulation of the geoid.
The bigger the geoid variations the less accurate the results are.
Characteristic Description