(e.g., within the DTM to be used) the SAR image 
coordinates of the anchor points are determined 
based on a reliable approach. 
2. The proper imagecoordinates of the anchor points 
are calculated from linear interpolation in between 
the image coordinates of step 1., using the actual 
terrainheight ( as interpolated from a DTM) as the 
argument for interpolation. 
Step 3 and 4: pixel interpolation: 
3. For minimum and for maximum terrain height the 
SAR image coordinates of the output pixels 
continuously are determined by bilinear interpolation 
within the corresponding output pixel block defined 
by 4 corresponding anchor points. 
4. The proper imagecoordinates of the output pixels 
are calculated from linear interpolation in between 
the image coordinates as stated under 3., using the 
actual terrain-height as the argument for interpola- 
tion. 
The orthophoto derived, may also be generated with 
a digitally determined coordinate grid, as well as 
edge or gradient enhancement procedures may be 
utilised to generate quasi line maps. At the Institute 
for Photogrammetry of the University of Hannover, a 
new standard product has been achieved for hilly 
terrain, in order to verify a reliable geocoding of ra- 
dar imagery for, e.g., GIS-input. The digital data is 
transformed into the GIS- coordinate system, which 
includes absolute positioning, north orientation and a 
uniform scale. The DEM- influences are already 
rectified, as well as changes in attitudes. 
4. QUALITATIVE ASPECTS OF RADAR 
IMAGE PRODUCTS 
Due to relative low geometric resolution, radar mis- 
sions for topographic mapping purposes should con- 
centrate on permanently clouded areas only. 
According to Ulaby the equivalent pixel size for, e. 
g., a nominal 6 m radar resolution for 5 looks 
approximately is 12 m. Therefore preferable high 
resolution radar should be flown. For further 
topographic applications it is highly recommended to 
compare samples of radar images with images from 
optical sensors, like conventional aerial photography 
of the same area, which for the most purposes gives 
an idea of the superiority of conventional aerial pho- 
tography for topographic detail interpretation ( in 
particular with respect to single buildings). The look 
direction must be chosen with respect to topography, 
taking into account the final appearance of the 
pseudo plastic effect in the radar orthophoto map. In 
order to overcome radar shadow, opposite side look 
direction radar in addition to same side stereo radar 
should be promoted. 
710 
For (digital) mosaicing purposes the acceptable de- 
pression angle, for image parts used for the mosaic, 
in particular depends on the topography. 
S. CONCLUSION 
The geometric approach used, should follow the ra- 
dar projection laws and not only empirical functions, 
like arbitrary polynomial equations. For the future a 
great improvement in this field is anticipated. Radar 
mosaics and Radar block adjustment can bridge areas 
with rare ground control points. If this gap extends 
about one strip width, polynomial equations used for 
an image to image registration, due to the error 
propagation, should be of first order. From house- 
keeping GPS the flight path data already can be 
achieved with acceptable accuracy, which within the 
radar block adjustment allows to use a more realistic 
formulation of the flight behaviour within the radar 
block adjustment procedure. Also inflight GPS will 
replace ground control to a great extend. 
6. REFERENCES 
Baker, S.R. and Mikhail, E. M., 1975: Geometric 
Analysis and Restitution of Digital Multispectral 
Scanner Data Arrays. The LARS, Purdue University, 
West Lafayette, Indiana. 
Doyle, F., 1975: Cartographic Presentation of 
Remote Sensor Data. Manual of R.S., pp. 1077- 
1106. 
Konecny, G., Schuhr, W., Engel, H. and Lohmann, 
P., 1984: Topographic Mapping from Space Borne 
Metric Camera Imagery. In: International Arch. f. 
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Konecny, G. and Schuhr, W., 1984: Practical 
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Konecny, G. ,Schuhr, W. ‚Engel, H. ‚Lohmann, P. 
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Konecny, G. and Schuhr, W., 1985: Linemap pro- 
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