7 
mounting parts. Deformations of that kind do not always act 
in a rotation-symmetrical way, so that they might in turn 
influence asymmetry as well. Exact compensation of affine 
deformations can be accomplished only if analytical resti 
tution methods are employed. 
In this connection it should be brought to attention that 
theoretically, the elimination of deformations in the image 
plane by means of optical aspherical compensation plates used 
on the plotting machine is possible only as far as these defor 
/nations are situated rotation-symmetrically around the image 
centre. Such compensation plates, in turn, are likely to be 
afflicted by similar engineering deficiencies importing new 
deformations. That is why in the case of photographs taken 
through modern, high-performing lenses, optical compensation 
plates frequently fail to yield the expected gain in plotting 
accuracy. 
Camera geometry 
The effective imaging function of an individual photogrammet- 
ric camera is described by the camera geometry. In addition 
to the properties of the lens system, the camera geometry com 
prises the influences of the camera body on image formation. 
These include the orientation and flatness of the focal plane 
frame, the flatness and stability of the vacuum back in film 
cameras and the operation of the vacuum mechanism. Air 
survey cameras are frequently exposed to extremal temperatures 
Fundamental studies of the temperature gradient behaviour in 
air survey cameras and its influence on the calibrated focal 
length have .been reported by U. Zeth (G.D.R.). 
External influences on photORrammetrie photography 
•^n aerial photogramme try, where photographs are taken from 
high altitudeq and through wide-angle lenses, refraction 
effects and earth curvature produce point dislocation in the 
image plane that may give rise to appreciable systematic