DISTORTION ANALYSIS 
The orthogonal correlator outputs are combined and 
multiplied by x and y reference waveforms whose instantaneous 
amplitudes specify the directions of the scanning spot. The inte- 
grated outputs of these multipliers represent the average x and y 
parallaxes between the two inputs. 
The x scale, x skew, y scale, and y skew distortion ana- 
lyzers use multiplier circuits similar to the parallax analyzers; 
in this case, the reference signals are integrated x and y wave- 
forms. 
The two zero-order and the four first-order error signals 
are fed to x and y integrators to provide sufficient gain for 
closed loop corrections. The integrators also incorporate a hold 
mode, where error signals can be stored for a short time in case 
a loss of either x or y information occurs. 
The x parallax error signal is applied to the z servo on the 
stereo plotter. The y parallax error signal, on the other hand, is 
applied directly to the y deflection amplifier of one cathode-ray 
tube to provide electronic correction of the y parallax. 
The first-order error signals from the integrators are ap- 
plied to the modulator to cause appropriate transformations to 
the scanning raster waveform. The modified scanning waveforms 
are added algebraically in the sum and difference circuit to pro- 
vide equal but opposite transformations to the left and right 
rasters. 
ADAPTIVE CONTROLS 
The main adaptive controls are: the channel selector, 
which controls the correlator frequency bands in use; the scan- 
ning pattern size control; the profiling speed or y velocity; the 
x-axis transformation loop gain; and the y-axis transformation 
loop gain. 
Correlation is initially established using image detail of low 
spatial frequency to secure a good pull-in capability, progressing 
to higher spatial frequencies to obtain higher accuracy. The size 
10 
of the scanning pattern is similarly reduced as correlation quality 
improves, and the profiling speed is increased. 
Simultaneous loss of correlation on both axes, such as 
might be encountered when entering a body of water, results 
in conditional failure in which the size of the scanning patterns 
are maximized and the instrument is driven at a fixed rate until 
correlation is reestablished, or until a specified distance has 
been covered. To provide a high probability of regaining corre- 
lation in the conditional failure mode, an automatic search in 
z is provided. By this means, correlation is reestablished auto- 
matically, even after traversing a slope or a discontinuity in 
height. 
A sudden drop in correlation quality produces a rapid 
shift to correlation of lower spatial frequencies, to a larger 
scanning pattern, and to a lower scanning rate. In extreme cases 
the y servo will cause the machine to stop profiling or even to 
back up while correlation is restored. A unique feature of the 
correlation system is that while the scanning pattern is com- 
pletely amorphous in its ability to detect image displacements, 
the quality of correlation can be monitored separately in the x 
and y directions. Loss of correlation in either axis separately 
does not produce failure, but results in the relevant transforma- 
tions being held at their existing values until correlation in that 
axis is reestablished. 
SERVOSYSTEM 
The z servosystem consists of a servoamplifier, dc torque 
motor, and a tachometer generator. The tachometer generator 
provides the rate feedback which stabilizes the servosystem in 
conjunction with the proper compensation network. Two dc 
signals are provided to the input summing points on the servo- 
amplifier: the tachometer rate feedback signal and the varying 
x parallax error signal, which produces the requisite z motion in 
the stereo plotter. 
The torque motor, tachometer generator, and servoampli- 
fier used in the y servosystem are identical to those used in the 
Z Servo.