10 
Correction of model deformations 
If we have to acknowledge that the effective systematic de 
formation of the optical model formed by relative and abso 
lute orientation is, after all, due to a number of causes 
still resisting quantification, it seems appropriate tp 
develop a correction model having corresponding degrees of 
freedom, the parameters of which can be determined from errors 
at known control points. Nothing in the analytical-photo- 
grammetric restitution process would impede the implementation 
of that principle, and some first, promising approaches have 
been made to eliminate systematic error causes in aerial tri- 
angqlation nets in that way. 
eliminate model deformations when using precision analogue 
plotters, the Jena instrument designers have been following 
that path, too. Compensation in the plotting equipment of 
optical model deformations is being effected by an electrical 
analogue computer both for planimetry and elevation. The 
device has degrees of freedom that allow to generate mutually 
independent cylindrical correction surfaces with x and y 
as their axes and being either concave or convex. The combina 
tion of both x and y corrections permits to generate ellip 
soidal surfaces of any desired orientation. Apart from the 
possibility to enter the operating parameters determining the 
degrees of freedom (which requires the causes of the model 
deformation to be known quantitatively), it is more important 
that the correction surface can be generated empirically by 
the elimination of discrepancies at control points of known 
coordinates. Practical experiences gathered so far have 
clearly confirmed the utility of the device and its highly 
welcome universality, which is lacking in optical compen 
sation plates r