de Diogon l:45 nr.1137337. f - 21 mm, h - 550mm 
microns Rodial distortion curves. 
+304 
+20 — 
+10 - 
r' mtm 
  
  
-10 + 
  
1:22 
EM EA 1:45 
theoreticol curve according to the monufacturer 
Fig. 11. Application of the grid method to the determination ot the radial distor- 
tion of a Biogon wide-angle lens for non-topographie photogrammetric purposes. 
Standard error of the distortion curves about microns. 
It is also of interest to investigate the relative agreement between the 
four different possible determinations of the distortion curve. 
From table 1 we obtain the four curves as demonstrated in fig. 5. 
Obviously there are also asymmetries present in the pencils of rays. 
In some more figures (6—10) the results of investigations of some 
other aerial cameras are demonstrated. In all investigated cases consi- 
derable asymmetries and irregularities of the pictures have been found. 
Only the radial distortion effect as determined from the average of the 
curves can be automatically corrected in connection with the plotting 
with the aid of wellknown correction devices. The remaining systematic 
errors (asymmetries etc.) have to be taken into account with numerical 
correction procedures. Of course, the significance of the errors has to 
be specially investigated. It is of particular interest to determine if the 
systematic errors are caused by the optical system or by the film base 
or perhaps by other circumstances. 
It is also of great interest to note that the influence of the 
atmospheric refraction and of the earth's curvature may change consi- 
derably with the flying altitude and with the opening angle of the 
camera. In [7] a theoretical investigation of these questions has been 
treated. 
Finally it has to be emphasized that the grid method gives more accu- 
  
rate 
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