error 
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 nor- 
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igure 
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Radial distortion according to the grid 
me thod 
manu facturer 
Fig. 2. Radial distortion of the Stereoplanigraph for base in 120 mm (above) and 
base out 120 mm, at a projection distance of 200 mm. c — 100 mm. The right 
projector. 
The fact that the same kind of lenses are used in the camera as well 
as in the projectors does not guarantee that the radial distortion will be 
compensated. It is well-known that different specimens of the same 
kind of lenses show quite different distortion curves. Not even if the 
camera and the projector lenses show similar distortion amounts, therc 
IS à guarantee of freedom from distortion effects. Investigations [4] 
have shown that to all appearances there 1s some difference between the 
distortion, determined in the laboratory, and the one obtained in aerial 
pictures. The curve used as comparison in the figures is based on labo- 
ratory determinations. Besides the radial distortion the lenses can be 
afflicted by other systematic errors. The tangential distortion may for 
instance be mentioned.