RELATIVE ORIENTATION 
Relative orientation is necessary to derive DTM coordinated 
in model space. Pass points are selected on the left photo 
in the traditional locations and correlated to conjugate 
imagery in the right photo. An analytic solution is then 
performed giving the relative orientation of the two photos. 
This facilitates location of the DTM points by enabling use 
of epipolar geometry which reduces the size of the search 
array containing the matched point. The principle of epi 
polar geometry states that conjugate imagery must lie along 
the line of intersection between the photo plane and the 
plane defined by the perspective centers and model point. 
Exploiting this principle enables a much smaller search 
array to be used thus reducing the computational time 
necessary to locate conjugate points. 
AUTOMATIC CONTROL PANEL RECOGNITION 
To enable the derived DTM coordinates to be transformed to 
the ground system, control points must be located and their 
photo coordinates determined. For a panel to be automati 
cally located, an array must first be synthesized which 
"looks like" the panel on the digitized photo. Since the 
panels can be in any orientation relative to the scan 
lines a single standard array is not sufficient and a means 
of simulating different scan line orientations is necessary. 
The method of resampling known as bilinear interpolation is 
used in conjunction with a two-dimensional conformal 
coordinate transformation to simulate the different 
orientations. A standard panel array, with the wings of 
the panel exactly coincident with scan lines is used as a 
basis to generate many possible orientations until one is 
found which is close to the actual orientation of the panel 
on the scanned image. The algorithm for finding control 
panels is as follows. First the standard panel array is 
lagged through the search array. If the minimum correla 
tion coefficient is unacceptable the standard panel array 
is rotated 45 degrees by means of the two-dimensional 
conformal coordinate transformation and the pixels are 
resampled. This new array is lagged through the search 
array and if the coefficient is still unacceptable further 
rotations are performed until an acceptable match is found. 
If after a specified number of trial rotations the panel 
has not been found the point is rejected. Once the coef 
ficient is within the threshold a fine tuning procedure 
is used to refine the location of the panel to sub-pixel 
coordinates. In the fine tuning process, parameters of the 
two-dimensional transformation are incremented or decrement 
ed one at a time by small amounts, the panel array is 
resampled and a new correlation coefficient computed. 
After a minimum coefficient is obtained by a series of 
incremental shifts of one parameter, the next parameter is 
incremented and decremented until a new minimum is reached. 
The order of the parameters refined is first rotation by 
two degree increments, then x translation, y translation 
and scale all in increments of 0.1. A contrast stretching/ 
reducing term is then varied in the same fashion and the 
whole process starts over with smaller increments of 0.5 
degrees for rotation, 0.025 for x and y translations, and