0.025 for scale. This two stage process produces a high 
quality refinement. During the refinement, the time 
necessary to compute the new correlation coefficient is 
drastically lower than the time necessary to lag the target 
through the entire search array. This is because the lag 
position giving the best match is already known and the 
resampled target array is correlated at this lag position 
only. After the refinement procedure yields the minimum 
coefficient, the x and y translation terms are added to the 
whole pixel location to give the sub-pixel coordinates of 
the panel. This procedure was also used for location of 
fiducials. 
The Mazomanie photography contained circular panels which 
are insensitive to rotation thus eliminating the need for 
rotation refinement. This reduces the time necessary to 
initially locate the panel in the search array. 
DIGITAL TERRAIN MODEL GENERATION 
DTM generation is done by selecting target arrays on the 
left photo in a regular grid pattern and correlating on 
the conjugate imagery in the right photo. Knowing the 
relative orientation parameters and approximate percent 
overlap of the photos allows reasonably accurate prediction 
of the search array on the right photo. In our test, for 
comparison purposes, DTM points were selected as nearly as 
possible to the location of points in the DTM read manually 
in the PG-2. 
When an acceptable match of the target array is found, the 
photo coordinates of the conjugate images are computed. 
Then the parameters of absolute orientation are applied to 
compute the ground XYZ coordinates of the point. If an 
acceptable match is not found, the target point is shifted 
slightly and the process repeated. This is done twice and 
if after that, the match is not found the point is rejected. 
Once all of the points of the grid are correlated, the 
coordinates are input to a contour mapping program and a 
topographic map is plotted. 
RESULTS 
Using the LaCrosse photography an area of approximately 6 
cm by 6 cm was selected in the left photo for DTM genera 
tion. This area was in the middle of a field where there 
were no trees present. The map resulting from this auto 
matically generated DTM is shown in Figure 3. Figure 2 
shows the map generated from the manually read DTM in the 
same area. These two maps show reasonable consistency in 
topographic features, however when they are overlaid, the 
one obtained from the automatically generated DTM showed 
elevations consistently higher than the stereoplotter map. 
Possible causes for this shift are scanner distortions, 
and inaccuracies of locating control points. The control 
points in this set of test photography were located 
manually by studying density overprints and were only 
good to the nearest whole pixel. This problem should be 
reduced with scanner calibration and control panel coor 
dinate refinement used with the Mazomanie photography.