The pull-in range of the orthogonal correlator, i.e., the 
displacement of the positive and negative peaks from the null, 
is 
d=+ millimeters 
i. 
4f 
If N is defined as the ratio between the maximum error 
signal voltage and the rms noise at the correlator output, and 
provided that the spatial frequency is within the correlator pass- 
band, the rms accuracy with which parallax can be cleared is 
ô = XL millimeters 
In practical correlation systems with an output bandwidth 
in the region of 100 hz, the output signal to noise ratio, N, with 
typical photographs is at least 5:1. 
It can be seen from Fig. 11 that a spatial frequency, f of 
20 cycles per millimeter is within the correlation bandwidth 
for scanning patterns less than 3 by 3 millimeters in size. There- 
fore, if N = 5, the expected rms accuracy is 
ô = 2.5 microns rms 
  
MN 
OPERATION OF AUTOMATED PLANIMAT 
The four operating modes are controlled by pushbuttons 
with indicator lights provided to show the mode in use. The 
buttons are normally operated in the following sequence. 
Standby-Manual. In this mode, the correlation system is 
inoperative and the servos are not connected. The manual z 
drive is coupled to the z carriage, and y speed is controlled by 
the y speed potentiometer. The x step mechanism operates 
normally. In this condition, the Planimat may be operated 
15 
manually in the normal manner, utilizing the floating mark and 
operator control of z. 
Orientation. The Electronic Correlator is activated in the 
orientation mode to assist the operator in clearing x and y par- 
allaxes in two ways: 
1.x and y parallaxes are displayed on center-zero meters 
visible to the operator. 
2. The x parallax may be cleared automatically by pushing 
the correlate button which connects the correlation 
loop and the z servo. 
Check Mode. In this mode the correlation loop is closed 
and all distortions are automatically corrected. The x and y 
drives are not connected, which enables the operator to move 
around on the model by directly moving the x carriage. This 
mode is useful for checking the performance of the correlator 
in doubtful areas and for manual override in areas where image 
detail is not adequate for automatic operation. 
Automatic Mode. After checking the model, the x carriage 
is located in the starting position on the model and the auto- 
matic button is pressed. The carriage is then automatically 
driven in the y direction, controlled by the correlator adaptive 
circuit, and steps automatically in x at the end of each strip. 
If correlation is lost in this mode, the system goes into the 
conditional failure state where the scanning patterns go to the 
maximum size, pattern distortions are zeroed, and profiling 
continues at a preset velocity. While in the conditional failure 
state, the scriber in the storage unit is inactivated and the pen- 
cil mounted on the x carriage of the Planimat is lowered onto 
the manuscript. If correlation is reestablished before the ma- 
chine has completed one full profile following the profile in 
which correlation was lost, the system reverts to automatic 
operation. If correlation is not detected in this interval, the ma- 
chine goes into conditional failure and automatically switches 
to the check mode. Lines drawn by the Planimat manuscript 
pencil show the positions where manual fill-in is required. At 
the end of the last strip, the system automatically returns to the 
standby condition.