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Reference image Subject image 
Figure 2. "La Grange" flow chart 
The program EVEN MORAVEC performs the CCP selection 
in the images using the Moravec operator as modified. The 
input for the program consists of the image file to extract 
CCPs from. The program must be run separately for the 
reference and subject images. Output is a text file containing 
a list of the candidate point image coordinates (line and pixel) 
and their interest values. 
The program TIN HORN is a correspondence program and 
operates in the "quick and dirty" fashion mentioned above. 
An improved correspondence strategy is currently being 
investigated which will avoid the foibles of the current 
algorithm. TIN HORN may, however, have a place in future 
versions of "La Grange," either in a modified version or as a 
complementary component of a more sophisticated 
correspondence scheme. The input for TIN HORN are the 
two CCP lists, one from the reference image and the other 
from the subject image, which have been created by EVEN 
MORAVEC. The output is a single text file containing the 
CCPs in each image which have been matched. 
HARDCORR is a program which correlates the CCPs to fine 
tune their locations in the subject image. It is derived from an 
already existing correlation package whose purpose was to 
generate parallax files from stereo images [Ehlers and Welch 
1987]. It takes as input the reference and subject images and 
the matched CCP list created by TIN HORN. The output is 
an ERDAS-readable GCP file containing the correlated 
control points. This file can be passed to the ERDAS image 
processing module for calculation of the transformation 
polynomial coefficients and resampling of the subject image. 
In addition to those programs shown in figure 2, there is 
also a display program to allow the user to visually inspect 
the locations and appearance of the CCPs after the selection, 
matching, and fine tuning steps have been performed. This 
is a useful tool for testing purposes and to demonstrate 
visually the process of CCP refinement to a final set of 
control points. 
PRELIMINARY RESULTS 
Each of the "La Grange" component programs have been 
tested individually. The source code from which EVEN 
MORAVEC and HARDCORR were written are known to 
have been thoroughly tested in their original form. 
Therefore, these programs have been tested mainly for 
debugging purposes. Program TIN HORN performs as well 
as expected (i.e. marginally) in tests. 
Combined testing of the entire "La Grange" package has not 
been thoroughly performed as of this report. Some initial 
testing has been done, however, using a small (256x240) 
subset of a Landsat TM band 5 image of an area near Tiger, 
GA. This dataset was used as the reference image and a 
slightly skewed (rotated clockwise approximately 8 pixels at 
each corner) copy of the it was made for use as a subject 
image (keeping in mind the limitations of TIN HORN). "La 
Grange" was then used to attempt to restore the skewed 
image to its original form. The following shows the results 
at each step of the matching process given the default user- 
input parameters: