Another area of difficulty with the present instrumentation in 
volves the inability to trace very tight contours; i.e., contours having 
very sharp bends. This has been found to be especially true when this 
condition exists on relatively flat terrain. This area of difficulty is re 
lated to the fact that, when a large rosette scan pattern is being used, 
it is possible for the contour to actually reverse direction within the 
area occupied by the scan pattern. As a result of this condition, it is 
not possible to derive a unique contour direction and, as a result, a 
loss of sterring signals results. While it is possible to reduce the size 
of the rosette scan pattern, the limitation cannot be completely overcome 
in this manner since the rosette pattern must remain relatively large to 
extract slope information on low-slope terrain. 
CONCLUSIONS 
The problem of automatically searching for, locking on, and 
tracing contours has been solved using a system of correlation circuits 
and electron-beam servoing techniques. The stereoplotter, in its 
present stage of development, can automatically locate and plot contours 
rapidly and with accuracies comparable to conventional manual techniques 
The solutions to the problems of automatically locating and tracing stereo 
model contours were proved to be both straightforward and workable. 
More work with the existing electronics will doubtless overcome the re 
maining contour-tracking difficulties. 
A radial spoke search pattern has been instrumented to demon 
strate the feasibility and practicality of an automatic search process. 
The pattern performs well and can sense almost any configuration of 
contours at any one elevation. 
The Stereoplotter, Projection AP-14 instrumentation lends it 
self to the automatic printing of the terrain planimetry. In this case, 
mechanical motion must take place. By profiling the model, moving the 
flying spot scanner tube up and down in the Z-axis to keep the scan ras 
ter always on the stereomodel surface, and by moving the flying spot 
scanner electron beam along the stereomodel Y-axis, using a small X 
scan, the imagery along a Y profile line can be printed on the display 
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