DIGITAL TECHNIQUES FOR MAP COMPILATION 
227 
Fig. 4A. Ortho-corrected photograph. 
digital process is ultimately limited by the 
quality of the input data, the scanner is a 
critical unit in the system. Hence, the image- 
to-digital conversion process is extremely im 
portant. 
The scanner was designed and built with 
the following capabilities: 
1. The system provides a means of pre 
cisely orienting stereo diapositives in the 
stereocomparator to permit accurate 
measuring and recording of fiducial 
marks, principal points, control, and 
pass-points in the two photographs. The 
conjugate measurements are recorded 
in terms of a photo-coordinate system 
and are entered as input digital data to 
the aerotriangulation program (resec 
tion and orientation). 
Fig 4B. Ortho-corrected photograph.