14 
Figure 14.--Fluor-0-Dodge contrast-control system for a 153/55 ratio 
diapositive printer. 
each phase are additive with each other and also with earth curvature. It is only 
by an analysis of the complete photogrammetric system that optimum distortion 
compensation can be obtained. The multicollimator camera calibrator of 
the U.S. Geological Survey is ideally suited to the analysis of complete photo 
grammetric systems. Figure 15 illustrates the angular position of one bank 
of collimators on the camera calibrator. The collimators are so positioned 
that a pair of diapositive plates made on the calibrator will produce a stereo 
scopic model from either wide-angle or super-wide-angle aerial photography. 
A summation of all distortion residuals, except earth curvature, can be directly 
measured in the stereoscopic model and used as a basis for the design of com 
pensation plates. 
The use of point-marking devices helps to eliminate errors of photoidentifica 
tion of control and passpoints, and makes the aerotriangulation process a much