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LEFT 
IMAGE O 
SIGNAL 
REGISTRATION 
ERROR 
SIGNAL 
  
IMAGES ALIGNED LEFT LEADING RIGHT LEFT FOLLOWING RIGHT 
  
Figure 11. Simple Registration Discriminator 
and Wave forms 
image signal is leading in time. 
3. Reversal of the scanning direction will re- 
verse the sign of the output since the lead- 
ing signal becomes the lagging one and vice 
versa. 
4. Misalignment in a direction at right angles 
to the direction of scan does not produce 
timing differences and will therefore give 
zero output. 
5. Under conditions of severe image misalign- 
ment, the image signals may be dissimilar 
to the extent of no correlation and no useful 
output. 
Figure 12 illustrates the registration dis- 
criminator as used in Stereomat. The balanced 
discriminator arrangement of two quadrature net- 
works and two multipliers is more efficient than 
the simple discriminator circuit in separating 
alignment signals from the effects of noise. 
——. x | 
p LI 
LEFT | 
IMAGE O—$—] FILTER —9—— 
SIGNAL | 
= 
1 Li 
2 
REGISTRATION 
-O ERROR 
Figure 12. Balanced Registration Discriminator 
Parallax Analyzer — Figure 13 
  
The direction of scan, using a random 
pattern, is constantly changing; therefore, the 
output of the registration discriminator changes 
even in the presence of a constant' alignment 
error. It is the purpose of the parallax analyzer 
to sort out the fluctuating signal from the regis- 
tration discriminator into steady X and Y paral- 
an EAS ELM ABRIR UFU 
AUTOMATIC STEREO(Appendix) 
lax signals. 
The diagram and table of Figure 13 illus- 
trate the action of the parallax analyzer. The 
output from the registration discriminator is 
separately multiplied with the X and Y reference 
signals, which are derived from the scanning 
generator and indicate the scanning direction 
at any instant. The low-pass filters smooth the 
output signals. The table summarizes the action 
of the parallax analyzer, with various combin- 
ations of scan and misalignment directions. The 
X and Y parallax signals are seen to be un- 
ambiguous and independent of each other. 
Slope Analyzer — Figure 14 
  
The slope analyzer uses the X parallax 
signal to evaluate the magnitude and direction 
of terrain slope. To facilitate slope detection, 
a circular motion is superimposed on the random 
motion of the scanning spot as described under 
Scanning Generator, On sloping terrain, the 
circular motion of the pattern produces a periodic 
fluctuation in the X parallax signal as the pattern 
centre orbits alternately above and below the 
terrain surface. The amplitude of this fluctuation 
indicates the magnitude of terrain slope. The 
time phase of the fluctuation with respect to the 
circular scan, indicates the direction or azimuth 
slope. 
In addition to the periodic fluctuation 
representing the terrain slope, random fluctu- 
ations, resulting from quantum noise and other 
disturbances, are also present in the output of 
the X parallax multiplier. Referring to Figure 
14, the filter passes the periodic fluctuation 
freely while suppressing to some extent the 
random fluctuations. Two multiplying correlators 
extract the slope signal from the remaining 
random noise. 
The T.S.D. signalis derived fromthe phase 
of the slope signal. Multiplying correlator B is 
used as a phase detector for this purpose. The 
output of the correlator is amplified and applied 
to a servo motor which rotates the shaft of a 
phase shifting resolver. The resolver shifts the 
phase of the circular scan signal at a rate of 19 
of phase shift for 19 of shaft rotation. The re- 
sultant signal is applied to the reference input 
of correlator B. Any change in the direction of 
the terrain slope changes the time phase of the 
slope signal. This in turn activates the motor 
to drive the resolver to the new position re- 
quired for phase quadrature. The position of the 
shaft of the phase-shifting resolver is therefore 
dependent on the direction of the terrain slope 
and is the required T.S.D. signal. 
The motor-resolver assembly is called 
the slope servo. The shaft of the phase-shifting 
resolver is coupled to the shaft of the steering 
resolver (Figure 5) and once the steering di- 
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adequate record of the discussion is available 
for publication. 
  
  
FROM 
X PARALLAX 
MULTIPLIER 
CIRCULAR 
CA 
SCAN 
SIGNAL