AUTOMATIC AND SEMI-AUTOMATIC MAPPING 
match electrically. To accomplish this, images 
are transformed into voltage-time series. 
The most exact match of the voltage-time 
series determines the z coordinate or the sur- 
face of the model at that xy point. There are 
several ways of approaching the determina- 
tion of this match. Included in these are 
phase-comparison, amplitude match, and 
area correlation. 
At the Engineer Research and Develop- 
ment Laboratories we have investigated 
these three in an effort to automatically pro- 
duce contours. 
[n 1950, the U. S. Army Engineer Research 
and Development Laboratories, Fort Belvoir, 
Va., entered into a contract with Bausch and 
Lomb Optical Company, Rochester, N.Y., 
to study the feasibility of producing contours 
automatically. This contract followed some 
preliminary experimentation by Bausch and 
Lomb on a suggestion by Dr. George Harrison 
of the Massachusetts Institute of Technology, 
and established the possibility of automatic 
contouring. With the equipment produced 
under this contract, it was possible to match 
successfully only artificial, high-contrast, 
stereo-projected diapositives. This instru- 
ment was profile follower with a phase-com- 
parison match using a short multiplex bar 
with two projectors. Since we did not want a 
60 cycle A.C. component in the scans, a D.C. 
Multiplex lamp supply was necessary. The 
scanning unit lay directly below the pro- 
jectors with the phototube control unit and 
phase meter directly above the lamp supply 
in a cabinet. The scanning chamber could be 
moved in three mutually orthogonal direc- 
tions. In operation it was set in x, driven at a 
constant rate in y, and controlled in z by the 
phase meter. In this instrument the profile 
was produced by a hot wire cutting a thin 
strip of plastic set in the model carving cham- 
ber, directly below the scanning unit. After 
the first profile was cut, it was used as a gen- 
eral guide for the scan on the second. The 
second was used for the third, etc. 
Looking somewhat more closely at the 
phase comparison-profile traverse approach 
in this instrument, we found that, primarily 
due to the heavy weight of the scanning unit 
and the relatively slow response in the servo 
system, the possibility of obtaining a reason: 
able speed of operation was limited. There- 
fore, in the next instrument phase, compari- 
son was abandoned in favor of amplitude com- 
parison. This instrument, constructed for us 
by Pickard and Burns, Incorporated, Boston, 
Mass., in outward appearance is very similar 
to the Bausch and Lomb instrument employ- 
ing the same multiplex frame and electronic 
cabinet, but its operation is quite different, 
amplitude matching and a directed xy-tra- 
verse. It was found that there was excessive 
noise introduced by the original optical-elec- 
trical transducer, and this was revised and 
later replaced by a translating pinhole. Since 
no profiles were being followed and since 
speed was a prerequisite, the data were re- 
corded on Teledeltos paper by means of cur- 
rent from the matching unit. The unit would 
be set in x and z and moved in y and every 
time a match occurred the paper would be 
marked. A change would then be made in z 
equivalent to the contour interval and the 
process would be repeated. 
Due to a number of reasons this did not 
prove to be the practical approach. 
Our next effort in automatic stereoplotting 
was directed toward a contour plotter which 
followed the area correlation approach. This 
instrument operated with a conventional 
Kelsh plotter and was built by the Hycon 
Company of Pasadena, California. The inten- 
tion was to scan a small area, and sense the 
direction of the contour. This tends to ap- 
proach more closely the action taken when a 
human being operates the machine. As he 
scans the model, the specific point is observed, 
but also the general surrounding area is taken 
into consideration. Although we had high 
hopes for this instrument, technical diffi- 
culties kept it from being successful. The 
main difficulty centered around the scanning 
head; however, there were also some circuitry 
problems encountered. The scanning head 
has been rebuilt by Hogan Laboratories, New 
York City, and we have corrected the cir- 
cuitry in our Laboratories. We are continuing 
investigations of this approach. 
While working on the approaches just men- 
tioned, The Photographic Survey Corpora- 
tion of Canada was also busy in this area. Mr. 
Gilbert Hobrough of that organization pro- 
duced a model instrument using a Kelsh 
plotter which demonstrated the feasibility of 
this approach to the problem. 
In place of the standard platen there was a 
scanning unit 12" by 10" by 18" high, which 
was mounted on ways permitting it to move 
in the x, y, z directions. The illumination driv- 
ing the automatic matching mechanism was 
derived from a flying spot scanner, installed 
with its face at the surface of the model, or 
rather at the spot where the face of the plat- 
ten would be. The blue light from the tube 
passed back up through the projector lenses, 
through the diapositive plates, and then on to 
dichroic mirrors which reflected the blue light 
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