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Glossary
Transformation
Characteristic
Advantage
Disadvantage
Twostep
Principle
Description
Three points: Tilted plane
•
through the three height control
points to approximate the local
heights.
More than three points: Best fit-
•
ting average plane.
•
Errors in height do not propagate
into errors in position since the
height and position transforma-
tions are separated.
If local heights have low accu-
•
racy or do not exist, a transfor-
mation 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 ellip-
•
soid and map projection is
required.
Parameters can be computed
•
with a minimum of points. Care
must 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 trans-
formation.
Restriction in the area over
•
which the transformation can be
applied. This restriction is
because 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.
Combines the advantages of the
Onestep and the Classic 3D transfor-
mation. It allows treating position
and height separately, but is not
restricted to smaller areas. Proce-
dure:
1057
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