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Stereo Matching fl 
• Lower level matching more effective for terrain modelling 
large homogeneous areas and abrupt depth 
discontinuities may cause difficulties 
• Matching at higher levels, say roofs, is easy 
roofs may be hard to extract 
• Combine matching and grouping operations 
• match at multiple levels and use matches to group 
• Use multiple images 
Scene Registration and Model Validation 
• Match a model with an image 
determine if structures are changed 
• Geometric relations useful for stationary structures 
• Global matching allows use of lower level features 
building validation system uses: 
• global matching of line features 
• higher level descriptions for validation 
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