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e. Eveluation of unique computer requirements and characteristics 
for on-line data processing. 
From this list the topics which are considered to be fundamental 
to the operation of the on-line System are the first two, or the 
automatic selection of pass points and the mathematical data reduction 
scheme. In the following sections these two items are discussed and 
algorithms for the implementation of these features on a computer- 
assisted comparator are developed. 
II. SELECTION OF IMAGE POINTS 
Before the data acquisition phase of aerotriangulation is begun, 
the image coordinates to be measured must be selected. In practice, 
the selection of pass points is empirical in nature and may depend on 
several factors such as, type of photography, quality of photography, 
accuracy requirements of the triangulation, and past production 
experience. 
Investigations into the quantity, quality, and photographic position 
Of pass points for aerotriangulation have been documented (3,8,9). The 
general assumptions made in all such research are that the image 
coordinates may be measured at any position on the photograph or that 
the "best" arrangement of points is known prior to beginning the 
acquisition phase. These assumptions may be too restrictive to 
accommodate the variety of situations found in on-line applications. 
For example, it may not always be possible to obtain image coordinates