building and updating 3D spatial database can 
be greatly improved because both the 
identification of polygons in edge data and the 
surface interpolation of the polygons can be 
easily automated. And the possibility of the 
extension of 2.5D surfaces to 3D surfaces in 
the SR model are also examined. 
3)A method of elevation interpolation are 
developed for the larger scale representation of 
urban space with a DUSM. It can represent 
several geometric conditions which characterize 
urban space such as the discontinuities of 
elevations as well as the steepness of slope. 
4)Through an example of the modelling, it is 
demonstrated that a SR model based on 2.5D 
surface is very effective in building a 3D spatial 
database. 
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