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REPORT OF COMMISSION VII 87 
modelle in einfachen Stereogeräten. Mitteilungen aus dem Geodätischen In- 
stitut an der Eidg. Techn. Hochschule in Zürich 1952. 
These treatises are contributions to the methodology of the interpretation of 
air photographs and give examples of geological and geographical evaluations 
from photographs. They deal with deformations of the pictures, stereroscopic 
observation, deformation of virtual spatial models etc. 
7) ,Flugbild der Schweiz”. Two hundred photographs by the Swiss Air (mostly 
large scale oblique photographs). The accompanying text (in German) is by 
Emil Egli, Peter Meyer, Walter Robert Corti und Edward Imbof. Mühlrad 
Verlag, Zürich 1949. 
E) SOME FURTHER REMARKS ABOUT AIR PHOTO INTERPRETATION. 
Recommendable exercises in reading and interpreting of vertical photo- 
graphs are: 
The comparison with corresponding low oblique and high oblique photo- 
graphs. 
The comparison of vertical photographs with good plans or maps of similar 
scales. 
More important than the use of air photographs commented upon for com- 
parison and of special interpretational keys is, in our opinion, a good power of 
observation, capacity of spatial imagination, but above all expert knowledge of 
the scope of the interpretation itself. Only the geologist is capable of interpreting 
an air photograph geologically. Only the plant geographer is able to interpret 
an air photograph competently as to its vegetational content. Only the student 
of agriculture can interpret an air photograph in its agricultural sense. Only 
the military expert is able to interpret an air photograph for military purposes. 
The interpretation of air photographs is not a branch of photogrammetric 
science and technique. It is rather like the reading of maps or of any other illus- 
tration of a landscape a help for all those who occupy themselves in any respect 
with the phenomena of the surface of the earth. In this sense should the air pho- 
tograph be propagated. Nevertheless it would be wrong to create a proper tech- 
nique or science out of the interpreting of air photographs. We can only give 
some indications as to the manner in which the reading of air photographs 
should be practised, how the photographs should be handled, and how stereo- 
scopic effects are to be obtained. Deformations of models are generally of minor 
importance for the reading and interpreting of photographs. 
The object of photogrammetry, of the technique of photogrammetrical 
instruments and photographs, however, is to give the best possible photomaterial 
to the interpreter of air photographs. About this, and in the sense of some of 
the questions contained in the question sheet some views and experience of the 
writer of this report may be added. 
1) Most favorable Flight Altitude, resp. best suited Scale of Image. 
Contrary to other authors I am against postulating a generally valid “most 
favorable Flight Altitude”. The most favorable flight altitude depends on the 
scope of the interpretation. The same applies to the scales of maps. 
2) Stereoscopic Exaggeration: Such is often desirable for flat areas to ren- 
der easily recognizable small, but for the purpose of interpretation important, 
height differences of the ground and also height differences, of trees, buildings