9 
Optical .compensating plates 
In the light of the above discussion, optical compensating 
plates are capable of correcting image point dislocations 
situated rotation-symmetrically around the centre, whereas 
they will not help to eliminate tangential and affine dis 
locations. Since radial deformation components in the modern, 
high-performance photogrammetrie camera lenses are extremely 
small and, on the other hand, because compensating plates 
may in turn cause deformations on account of unavoidable 
manufacturing tolerances, the use of such plates will frequent 
ly fail to improve restitution results. Attempts to compen 
sate rotation-symmetrical dislocation components resulting 
from earth curvature and atmospheric refraction are compli 
cated be the necessity to employ different plates for changing 
flying altitudes. 
Reseaua 
The idea behind a reseau image superposed on the picture 
during exposure is to derive from the known (calibrated) 
nominal positions of the reseau crosses and from their actual 
coordinates measured in the photograph corrective interpola 
tions for all image points measured. The measurement of the 
reseau points on a comparator means considerable extra work. 
Such a method will be restricted to analytical restitution 
techniques. Comparing the results of practical applications 
of standard-type and reseau cameras, the so-called "Oberschwa- 
ben H test revealed no significant difference. This should be 
interpreted as a positive establishment of the fact that 
errors of interior camera geometry (which alone can be correct 
ed by a reseau) are, after the transformation of the obtained 
qoo^dinates to known control positions, of secondary impor 
tance compared to external influences on photogrammetrie 
photography.