Mv 4 . 
photograph at the desired image location, and then 
adjusts each slave photograph, in turn, until X and Y 
parallax are removed. For automatic fine pointing, 
the operator locks the master photograph as before; 
he then presses a control panel switch that commands 
a special automatic fine-pointing computer-correlator 
routine to adjust the unlocked slave photograph. 
When the automatic adjustment is completed, the 
operator repeats the operation for the other slave 
photograph. 
To record the image coordinates of the selected 
point, the operator may elect to accumulate several 
pointings of the same image or to record the single 
pointing. He presses a control panel switch to initiate 
the recording routine in the digital computer. The 
editing procedures described earlier are carried out 
automatically by the computer program. When the 
recording routine is completed, the coordinates are 
punched on a card, or an alarm light on the control 
panel notifies the operator of an inconsistency in the 
image coordinates. The coordinates are recorded with 
1 micron as the least significant digit. 
When reseau materials are being used, they are 
identified to the computer program at the time of 
interior orientation. The stage coordinates of two 
reseau marks are observed at this time. When the 
program enters the recording routine during pass- 
point measurement, the routine checks for reseau 
materials on each stage. If reseaus are present for a 
particular stage, the computer program calculates the 
reseau square in which the pass-point lies, then checks 
to see if each reseau mark has already been observed 
by the operator. If a reseau mark has not been ob- 
served, the program calculates the approximate stage 
coordinates of the reseau mark, drives the comparator 
stage to those coordinates, and turns out the stage 
lights for the other two stages. The operator simply 
turns the handwheels to center the measuring mark 
AUTOMATIC COMPARATOR 
directly over the reseau mark, and presses a switch to 
record the coordinates. The computer program then 
goes on to consider the next reseau mark. Thus, the 
operator’s mark-reading task in working with reseau 
materials is limited to only those reseau squares that 
surround selected pass-points. No confusion is pos- 
sible as to which reseau mark to observe, and the final 
photo coordinates of the pass-point are adjusted for 
the reseau-mark displacements before recording takes 
place. 
SUMMARY COMPARISON 
Table 1 summarizes major features of the Auto- 
matic Comparator and compares them with features 
of a conventional comparator. 
Table 1 Summary Comparison 
  
CONVENTIONAL 
STEREO COMPARATOR 
AUTOMATIC 
COMPARATOR 
  
Hardware-Controlled Operation Program-Controlled Operation 
  
Continuous stereo model 
maintained throughout 
overlap area 
Manual stereo adjustment at 
every point 
Stage coordinate measurements True photo coordinate 
measurements including 
reseau correction 
On-line determination and 
display of measurement 
precision 
Measurement precision unknown 
until subsequent data processing 
Optional optical or video- 
stereo viewing 
Optical viewing only 
Optional automatic or manual 
point-transfer 
Manual point-transfer 
  
  
  
  
89