mina-
limbs,
to 101
I Case
image
points
exte-
previ-
1996).
IDA's
Single
ure of
elimi-
oints.
inates
model
1erical
W, z-
ted in
M was
4x4
ations
imum
ror 91
errors
areas
phi
0 50 100 150 290
+
elo. 7 $
+ +
tu"
?
theta
100T
1204
Figure 8: Position of errors > 600 m in the DTM of IDA
where reference points are not available. In these regions it
is obvious that the given reference points cannot represent
the surface adequately.
5 CONCLUSIONS AND OUTLOOK
In this paper we have presented an efficient hierarchical
method for global DTM modelling, which makes use of a
sphere as reference surface. It is based on the principle
of series expansions and employs locally supported basis
functions. The crucial point is the explicit computation
of the error on each level which allows the adaption of a
regular grid to a given arbitrary set of reference points.
Digital terrain models of Australia and part of the asteroid
243 IDA, demonstrate the power and flexibility of the new
approach.
Further extensions concern the usage of reference points
with different accuracy, e.g. including control points mea-
sured by an operateur. Each reference point can be
equipped with an additional weight in the summation (3).
In connection with the applications in Geodesy, Geology
and Photometry, the calculation of the normal vector to
the surface as well as the modelling of local features (e.g.
craters) are very interesting (Duxbury, 1991).
6 ACKNOWLEDGEMENTS
In performing this study we received valuable support by
Jürgen Oberst and Bernd Giese at the Institute of Plane-
tary Exploration of the DLR, which is gratefully acknowl
edged. The authors thank Wolfgang Zeitler, Institute of
Planetary Exploration of the DLR, for doing the image
matching.
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
