expected that this technique, called '"orthoprojection', will have 
uses in architectural work as well. The first experiments made 
by several institutions have supplied good results and have en- 
couraged continuing research in this field. 
In the following a description of the special process for producing 
orthophotos in architectural photogrammetry is given. Included 
to this report are the results of accuracy and efficiency tests. 
The examples of orthophotos enclosed give an idea of possible 
applications. 
2. Orthophoto-production in architectural photogrammetry 
Because of the heterogeneity of different objects the production 
of orthophotomaps in architectural survey requires a detailed 
design of the project parameters for photography and orthopro- 
jection. All terrestrial cameras and orthoprojection systems are 
qualified more or less for architectural purposes. 
2.1. Photography 
Project planning begins with the selection of a suitable camera. 
Here the focal length, i.e. the angular field, is of special im- 
portance for the accuracy and the image quality of the resultant 
photomap. From the orthoprojection process arises a number of 
errors which are caused by the operator, the object and the recti- 
fication system itself. System errors as a result of height dif- 
ferences inside of the rectification element, profiling errors, 
image motion and radial displacements all depend on the angular 
field. Smaller aperture angles or larger focal lengths reduce 
the mentioned errors. If small-angle cameras are not available, 
the image field of wide-angle photography should be restricted. 
The arrangement of the photogrammetric survey also influences the 
subsequent orthoprojection. Large differences in height with 
regard to the Z-range of the instrumentation later used should 
be avoided. This problem is resolvable by a greater camera-to- 
subject distance, which, however, can be obtained only in a few 
cases. One should also take care that protruding parts of the 
object will not be imaged at the border of the photograph. These 
arrangements, which improve the quality and the accuracy of the 
orthophoto, extend on the other hand the number of photogrammetric 
models. With more experience in this field a compromise between 
accuracy and economy will certainly be found.