11 - 
AUTOMATIC SEARCH SYSTEM 
The purpose of the search system is to automatically locate and 
follow any stereomodel contours that exist for a particular elevation in 
model space. 
The search pattern selected is a compromise between efficiency 
and ease of instrumentation. The pattern consists of a series of straight- 
line searches which radiate (1) from the center of the flying spot scanner 
tube during the first mode of operation and (2) from the edges of the scan 
ner tube inward toward the center during the second mode of operation. As 
a stereomodel contour is printed, as a result of one search line, the search 
pattern will resume with the next sequential search line. 
Digital circuitry is predominantly used in instrumenting the auto 
matic search system. Analog operations on selected digital pulses provide 
the required wave shapes for search deflection. The search system instru 
mentation provides eight spokes searching outward from the scanner tube 
center in a linear fashion, followed by four spokes searching from the edge 
of the scan cathode-ray tube inward to center. Crossing a contour inhibits 
the search generator so that, when it is restarted, the search sequence is 
continued. After the entire search pattern has been completed, the search 
system stops; and a visible light indicates to the operator that a new ele 
vation setting is required in the stereomodel. The search sequence of the 
rosette scan pattern is shown in Figure 4. 
CORRELATION TECHNIQUES UTILIZED IN 
CONJUGATE IMAGE MATCHING 
Correlation techniques are utilized to indicate a match of conju 
gate image points from a stereo diapositive pair. The detection of such a 
match is fundamental to the problem of locating and tracing stereomodel 
contours. 
The general correlation function is given by: 
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