normally used only in a few copies. Therefore photographic repro- 
duction is possible, 
2.4. Problems in application of orthophototechnique in architec- 
tural work 
Although the scope of application in this field can be extended 
considerably both by detailed planning and by the best possible 
utilization of the instruments, there still remains a type of 
surface to which orthophototechnique should not be applied. 
These are subjects composed of staggered planes and protruding 
elements which cover other details. Buildings of this type are 
antique temples, porticos, gothic cathedrals or, for example, 
churches in the baroque style. They cannot be represented by 
orthophotoplans in general. Only parts of these objects such as 
cupolas, frescos, paintings or facades are suited to differential 
rectification. The decision as to the type of representation 
depends upon the object and should be made before starting 
photogrammetric work. 
3. | Accuracy 
The accuracy of orthophotomaps in the architectonic field depends 
upon the precision of terrestrial control, on photographic image 
formation, system and profiling errors in orthoprojection and on 
the accuracy of the reproduction processes. The final accuracy 
is to be regarded as an accumulation of the single influences and 
can be evaluated in this way. All the figures given here refer 
to the object scale. They originate from extensive tests carried 
out at the Photogrammetric Institute of Stuttgart University. 
Every photogrammetric work is based on control points. In archi- 
tectural survey these points can be given within an accuracy of 
+ 1 tot 10 mm. Errors of image and model formation amount to 
+ | mm each, again in reference to the object. From orthoprojec- 
tion arise coordinate errors of about + 10 mm on the average, 
which is equivalent to 0.15 mm at a mean orthophoto scale of 1:70. 
This value includes errors of connexion and orientation in the 
orthoprojection system, deviations in profiling caused by the 
operator, as well as system errors resulting from the degree of 
model approximation. 
If. polyester fortified paper of great dimensional stability is 
used in the copying processes, errors of + | mm in the object 
are expected. Regular photographic paper changes its size depend- 
ing on humidity and temperature so much that it should not be