The DEM points are then computed by simple formulas. In each case X, Y, Z are 
related to the left image, M and P represent magnification and principle distance, Q 
the tilt angle. For most users' purposes parallel projection formulas (a) will suffice, 
(a) X = xy / M 
2. X cosa - x, 
M sin a 
while higher accuracy demands will be satisfied by (b) - giving central projection - , 
if images are recorded with low magnification. 
(M PY (xj cos a - x) + MP x, X, sin a 
  
  
  
(b) Z = 
M (( (M PX + x x.) sina + MP (à x) cosa ) 
: M P. 
x .. ME-MZ v MP-Mz 
I M* P l M* p 
The computed points just as the contour lines interpolated from the points are 
superimposed on the stereo model. Thus the operator can decide, whether work is 
done correctly or not, for sometimes gross errors in finding corresponding points 
cannot be avoided. The points and lines are stored in a data base. Editing features 
for efficient correction and updating of current results are under development. 
Particular efforts will be made to apply the multiple correlation, using additional 
data of the same object (e.g. recorded with other tilt angles). 
Two examples of graphical output of DEM data from SEM imagery are shown in 
figures 5 and 6. 
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