206 
After computing the image seqences in world coordinates, a central projection is exectued to get the positions in 
the camera coordinate systems. The results are two synchronous sequences of particle positions, one for each 
camera. 
An error in the particle tracking typicaly results in a break in the trajectory. Thus the number of breaks are used 
to examine the influence of the pariticle tracking on the stereo correspondence. 
Sequences with densities up to 3000 particles have been used to test the reliability of the stereo correspon- 
dence algorithm. 
Figure 3 shows a sequence with 1500 particles and a length of 40 images. The upper half represents the right 
camera and shows all trajectories, while the lower half shows only the corresponing trajectories in the left ca- 
      
         
  
    
        
     
         
    
  
  
  
  
   
  
  
    
  
  
  
  
  
    
     
   
  
   
  
   
     
        
        
  
   
        
  
   
  
   
   
  
     
   
  
  
  
     
     
  
   
   
  
  
  
        
      
  
             
  
  
  
  
  
  
      
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Figure3 Simulated sequence with 1500 particles 
6.3 Results 
The simulations showed, that the quality of the stereo correspondence at high particle densities (» 1000) de- 
pends mainly on two parameters: the quality of the particle tracking and the exact knowledge of the epipolar line. 
Simulating an error free particle tracking (0X breaks) the correspondene could be solved for 1300 particles at a 
matching rate of about 65%. Simulating a worse particle tracking (36% breaks) up to 850 correspondences 
could be found. 
The above results have been evaluated using an epipolar search rectangle of the same size as in an experimen- 
tal setup. Using a polygon as the search area results in a more accurate estimation of the epipolar line. This can 
be simulated reducing the size of the search rectangle. The results are then 1900 correspondences at a matc- 
hing rate of 8875 (OXbreaks) and 1700 correspondences at matching rate of 77% (36%breaks). 
’ 
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop “From Pixels to Sequences", Zurich, March 22-24 1995