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also eliminated during this process in order to maximize correlation 
between the photographs and thus improve the accuracy of the other 
correlation measurements. 
Automatic Profiling 
Actual plotting can be performed automatically in either a 
profiling or a contouring mode, using information supplied by the 
correlator to control elevation. Additional data is also entered into 
the computer by the operator prior to initiating the operation. In the 
case of profiling, for example, this data includes: 
(1) Desired direction of profiling 
(2) Spacing between profile lines (both in the stereo 
model and on the coordinatograph) 
(3) Boundaries of the area to be profiled 
(4) Plotting scales 
(5) Desired elevation accuracy 
The direction of profiling may be any desired angle with respect 
to the model coordinate system. If profiling of the entire model is not 
desired, the boundaries of a selected area may be entered in terms of 
the distances of the four boundaries from the center of the model. The 
selected area must be a rectangle, oriented in the direction of the profile 
lines. If no boundaries are entered, the computer automatically termi 
nates each profile line when the edge of the photograph is reached. 
In this system, the rate of change of terrain slope is a major 
factor in determining accuracy at any given profiling rate. This 
quantity is monitored continuously. If it exceeds a prescribed level, 
plotting speed is reduced automatically to assure that the desired 
accuracy is maintained. Plotting speed is also reduced under poor 
photographic conditions, such as low contrast or low image detail, or 
when the measured parallax errors exceed the desired accuracy. 
Automatic Contouring 
Contouring is performed in much the same manner as profiling. 
Data which must be entered into the computer prior to the operation 
includes :