After tracing the contour, the system automatically returns to the search 
mode and resumes the search mode sequence. 
The display, or contour map manuscript, is prepared by photo 
graphing a display cathode ray tube whose electron beam is caused to 
move in synchronism with the DC position of the center of the flying spot 
scanner tube beam. The display beam is also activated when the level of 
video signal cross-correlation exceeds a preset level and, therefore, is 
turned off except when actually tracing a stereomodel contour. A one-to- 
one copy camera photographs the display cathode-ray tube, thus producing 
a contour manuscript at stereomodel scale. 
PHOTOSCAN SYSTEM 
The purpose of the photoscan system is to scan each diapositive 
forming the stereomodel and derive electrical signals from the diapositives 
which are functionally related to the photographic imagery contained in the 
scanned area. 
To fulfill its purpose, the photoscan system must effect the re 
quired conversion of the photographic detail to electrical signals at a high 
rate of speed. All of the fine detail photographic information contained in 
a diapositive set must be completely transformed. After transforming the 
photographic imagery to wide-band electrical signals, the correlation sys 
tems utilize this information to automatically locate and track existing 
stereomodel contours . 
Basically, the stereoplotter's photoscan system consists of the 
following components: 
1. A flying spot scanner and associated scan raster generator. 
2. A modified Gamble/ Balplex projection plotter. 
3. Receiving photomultipliers and wide-band amplifiers. 
The flying spot scanner scans each diapositive from the stereo 
model area which the tracing table conventionally occupies. The scanner 
generates an intense point of light, a few thousandths of an inch in dia 
meter, which the Balplex projection optics further reduce. The resultant 
demagnified scanning spot can resolve 37 optical lines per millimeter in 
the diapositive emulsion plane.