SESSION 8: 
  
AREA BASED MATCHING TECHNIQUES 
  
  
CHAIRMAN: W. Fórstner (FRG) 
AUTHORS: A. Grün and E.P. Baltsavias (Switzerland) 
TITLE: HIGH PRECISION IMAGE MATCHING FOR DIGITAL TERRAIN 
MODEL GENERATION 
DISCUSSION: 
Ehlers (USA): 
  
Baltsavias: 
I have two questions. As I understood, this is an 
interactive process. You select certain areas 
around points of interest in one image and try to 
match them with the same area in the other image. 
Have you done anything to find those "points of 
interest" by automatic techniques? And the second 
question is: You used interpolation techniques to 
create a regular grid based digital terrain model? 
And what are your further plans for DTM generation? 
I have already mentioned that this was a project in 
cooperation with the firm Wild. So, we had some 
specifications to follow. The specifications were 
that we should determinate the height at given X 
and Y ground positions. So, to answer your second 
question, in this case you don't have to interp- 
Olate. After you determinate the heights, you have 
a regular grid on the ground. Now, of course, what 
you mentioned is correct. I mean that it is an open 
subject, whether we should follow this approach or 
follow another approach which chooses the best 
points for height determination and then using 
these, which would not probably be a regular grid, 
interpolate to a regular grid. That is correct, I 
agree with you. As far as your first question is 
concerned the points we chose were not really points 
of interest, in the sense that they had good geo- 
metric and radiometric properties for precise height 
determination. We just chose some points, ranging 
from good to bad, so that we could measure them at 
the AC1, and were able to compare the heights from 
the manual measurements to the heights from the 
matching algorithm. The choice of points of inter- 
est was out of question for this project, since 
we were constrained to determine the heights at 
given X,Y positions. 
Grün (Switzerland): I just would like to add to your first ques- 
  
tion. It was not really an interactive process. 
That was exactly the reason why we could not really 
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