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a relative orientation including data snooping will be computed. Blun- 
ders or large discrepancies can be checked by typing the point index, 
which causes a setting of the named point by the analytical plotter. 
Based on the relative orientation, model coordinates are computed. The 
model is transformed to the cumulated models before to a strip and the 
neighboured strip is transformed to it. The transformation of the strip 
will be done two-dimensional, because this will not imply the necessity 
of a dense distribution of vertical control points, but it limits the 
power of the test. Off-line trials have shown, very often not enough 
vertical control points are available for a three-dimensional combina- 
tion of strips or subblocks and also a bundle block adjustment has a 
very limited power of the test for the photo model, which just has been 
terminated because the at last measured model is located in any case at 
the corner of the subblock. Only in the case of 60 7 sidelap a suffi- 
ciant check is possible by bundle block adjustment, but for increase of 
cost-effectiveness it is better to measure at first only a subblock with 
20 % sidelap and after this, the strips between. 
4. OPERATIONAL ASPECTS 
The possibility of analytical plotters of computer supported pointing 
has a strong influence to the structure of blocks. The use of mono or 
stereo comparators for photo measurements is very time consuming. The 
photo points have to be identified and the setting has to be done by 
the operator without any support. By this reason, the number of measure- 
ments was minimized and blocks with endlaps of 60 % and sidelaps of 
20 % - 30 % have been used. That means, a high number of points have 
been measured only in 2 photos and so the reliability was poor. If we 
always have some information about the location of points, this can be 
used for computer supported pointing. The data aquisition will be 
speeded up because the operator only has to make the final exact point- 
ing without searching the point and without typing the point number. So 
it will not increase the time for data collection so much, if the side- 
lap is raised to 60 Z and even if crossed strips are used. An extended 
overlap includes more photo measurements for each object point which 
raises the accuracy, especially for the height and what is often more 
important, it improves the reliability. 
In the University Hannover aerotriangulation block have been measured 
for purposes of cadastre and for inspection of subsidences in coal 
mining areas. For both cases highly accurate and reliable results are 
necessary. The flight planing was made with 60 % endlap, 60 % sidelap 
and crossed strips with also 60 % sidelap. Each point should be at least 
in 8 photos. This high overlap would cause in the case of measurement 
with comparators 4 times of the effort like for a single block with 
only 20 % sidelap. In a first step, with the analytical plotter only a 
block with 20 % sidelap and minimal strip connection was measured. In 
the overlapping area of neighboured photo models, an automatic pointing 
with the photo coordinates of the model before and similiarity trans- 
formed photo coordinates to the new photo was done. 
A digitizing of contact prints with identified points can speed up to 
measurement and raises the capacity of expensive analytical plotters by 
use of unexpensive digitizers. A preliminary block adjustment delivers 
object coordinates of all points. Based on these coordinates, the other 
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