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Chapman, David 
  
are degraded at incident angles within 10 degrees of the surface normal. However sufficient data is normally acquired 
away from these regions to enable a realistic surface recovery. Evidence of such systematic effects can be seen in the 
pattern of residuals visible in surface fits to both planar (figure 9) and cylindrical data (figure 10). 
  
  
  
Figure 5. Results of random sampling for user defined 
region of interest (ROT). The operator first specifies a 
ROI for a plane fit to the rear wall, points on the wall 
are identified by the random sampling routine that 
determines the plane parameters and marks the points 
as used. Next a ROI for the foreground cylinder is 
defined. 
  
  
  
  
  
  
Figure 6. An alternative approach to the extraction of 
the pipe using an iterative refinement of a best fitting 
quadric based upon a user-defined seed point (figure 
6a) and a pre-defined rejection threshold. 
Figure 7. Residuals to initial quadric fit subsequently refined by the least-squares determination of the best fitting 
cylinder. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 127