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Eckart Michaelsen 
  
compared e. g. our system to one other shell and approach, that we know well enough to dare so. The current backlash 
in the field of structural recognition methods may be explainable to some degree by the difficulties mentioned. But for 
some tasks, there may be no other way out. 
Complex models with many degrees of freedom permit classical one-step template matching (with tolerable effort) only 
if there is enough prior knowledge (e. g. from maps). Otherwise perceptual grouping of object parts seems to be the 
only reasonable alternative. This gives best results if an alternation is implemented between grouping and matching. 
Generic models pose the most severe performance problems because of their inherent combinatorics. We discussed this 
with an example of grouping buildings and roads into settlement structures. But computational complexity is only one 
of the difficulties encountered. There are some other serious problems of which the applicator should be aware, if he or 
she is confronted with a task, that appeals for such a method. Our advice is to check the list of problems with respect to 
the special task, before one decides to use one of the alternatives mentioned in Sec. 4.1 or something else. 
We do not want to discourage anybody. Perceptual grouping and model based recognition remains a fascinating and 
promising discipline inside computer vision. The more problems you encounter the more ambitious becomes the topic, 
and awareness of the problems helps to find clever solutions. 
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