then 
uses, 
1etric 
lition 
X, y) 
bove, 
black 
y, as 
sition 
hows 
th all 
Zuxun Zhang 
b 
  
Figure 5. Precise position result 
of gable roof 
  
Figure 6. Enlarged image and the result 
4. Conclusion ; of precise position 
Through the preparatory test, the mathematical model of semi-automatic house extraction has been approved as correct. 
Besides its perfect geometric accuracy, its geometric constraint condition in object space enables it to prevent the noise. 
For example, neither the boundary or individual corner point in shadow, nor the low contract of some boundaries of 
houses (weak boundary), could affect the final results. 
In next research work, besides the improvement of the mathematical model mentioned above, the ability and range of 
automation should be increased, in order to consummate the semi-automatic house extraction step by step. These will be 
the most important content of the study for digital photogrammetry workstation. 
ACKNOWLEDGEMENTS 
We are grateful to the support from Natural Science Fund of P.R.China (No. 49771063). 
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 1025