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the screen, and can be used as a conventional
floating mark. Upon releasing the button, the
spot continues scanning.
Non-Projection Plotters
Non-projection plotting instruments employ
separate optical systems for viewing each stereo
plate, generally orthographically. Itis convenient
therefore in applying Stereomat to these in-
struments, to use a separate C.R.T. for scanning
each plate. There are other advantages in using
separate scanning patterns,even for projection
plotters, as discussed later under "Mode! Slope
Limitations”.
The left and right reference marks, in a
non-projection plotting instrument, are “fused”
by the operator into a floating mark having both
vertical and horizontal position. Likewise the
left and right scanning patterns in a non-pro-
jection stereomat, combine to produce a pattern
having vertical and horizontal position. Re-
ferences in the text to "scanning pattern” apply
equally well to the combined pattern of a non-
projection Stereomat.
Signal Flow
Figures 4 and 5 are block diagrams of the
complete Stereomat, and show the relations be-
tween the various functional units for the two
basic modes of operation. Most functional units
are common to both modes, the differences being
in the utilization of the data signals from the
correlation unit.
The scanning generator supplies deflection
voltages to the coils and reference signals to
the correlation unit. The reference signals in-
dicate the components of scanning velocity in
the X and Y directions at any instant.
Image signals from the two photo-cells are
processed by the correlation unit and translated
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Figure 3. Optical Duplexer
AUTOMATIC STEREO
into five separate data signals.
Tracing Velocity signal.
X parallax signal.
Y parallax signal.
Terrain slope magnitude (T.S.M.) signal.
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Terrain slope direction (T.S.D.) signal.
The T.S.M. signal is fed back to the scan-
ning generator to control the size of the scanning
pattern. The remaining data signals direct the
mechanical motions required to orient, contour,
or profile the model.
Parallax Sensing
The correlation circuits sense parallax by
detecting time differences between the signals
from corresponding parts of each image and the
signals are limited sharply to eliminate amplitude
variation. The operation is thereby rendered in-
sensitive to changes in either average density
or contrast of the stereo plates.
To sense parallax by time differences, the
spot scanning the images must have a component
of motion in the direction of parallax; otherwise
no time difference is produced. Since the di-
rection of parallax may not be known, the spot
should scan the images in various directions to
explore all possibilities. Figure 6 illustrates
some of the scanning patterns that have been pro-
posed from time to time for stereo sensing. The
random pattern was chosen for the following
reasons:
1. The images are scanned in all directions.
2. The irregular and constantly changing pattern
does notreact with image configurations such
as lines, circles, etc., to produce spurious
data signals.
3. Tbe velocity of the spot varies over wide
limits, thereby emphasizing fine and coarse
image detail alternately.
4. A random pattern is relatively easy to produce
electronically by means of amplified " tran-
sistor noise".
Relative Orientation — Figure 4
Separate motors are provided for the Kappa,
Phi, and Omega axes of the two projectors, and
the amplified Y parallax signal is applied to the
orientation motors through separate push-button
switches. The operator moves the C.R.T.
carriage to one of the "parallaxing stations" and
presses the button energizing the motor ap-
propriate to that station. The motor causes the
projector to rotate about the required axis so as
to reduce parallax, the action ceasing when the
parallax signal is no longer great enough to drive
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