Based on experiences with numerous test cases similar to those described 
here, a design feature of the current program is a strategy definition 
option, in which the user may define the sequence of steps, the 
acceptence/rejection criteria, and the window size/shape parameters which 
will be used for the estimation of each data point. This strategy 
definition can be modified to suit the image texture characteristics, and 
the terrain characteristics for a particular project, or set of 
photographs. 
With regard to item (2) there are several possibilities which are being 
studied. One could possibly pre-sample the photographs before scanning for 
correlation, to determine which areas have sufficient information content 
for matching. In order to better interpret data which has been collected 
one could record a "figure of merit" to indicate the ccnfidence that we 
have in the elevation value. This could be used for weighting in a post- 
processing interpolation step to strengthen weak points or to fill in 
where the quality of correlation was very poor. A threshold level of this 
figure of merit could be used to trigger a manual re-observation of the 
point in question. This would fit well into a strategy where an entire 
model is scanned without operator intervention, and then all of the manual 
assists are performed at the conclusion of the automatic scanning. Another 
possibility which is being considered is to manually observe a sparse DEM 
grid over the model prior to scanning for correlation. The scanning 
program could then obtain, by interpolation from the sparse data points, a 
reasonably gocd approximation of the terrain height at each of the final 
grid points. 
CONCLUSIONS 
The tools are at hand for applying the techniques of digital image 
processing to numerous measurement tasks currently performed manually by 
stereo operators. The design of the DSR11 has permitted easy integration 
of video acquisition hardware. Such hardware is extremely flexible, and 
new applications usually call for only new software, without modifying the 
instrument itself. 
The ACOR system has been shown to produce good terrain elevation data when 
the requirements of image definition and terrain slope are met. Many 
enhancements and alternate image matching techniques are being actively 
studied both within the Kern company and by other independent researchers 
working with this same equipment. The system, which is already usable for 
much photographic source material, should become even more accurate and 
reliable. 
REFERENCES 
1. Cogan, L. and Hunter, D., "DIM Collection and the Kern Correlator", 
ISPRS, June 1984 
2. Bethel, J., "The DSR11 Image Correlator", ASP Proceedings, March 1986 
568