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4.2 Data Structure Conversion 
There have three kinds of data structure conversion 
algorithms in our 3-D GIS. One is an algorithm from TEN 
to Octree, which is vector to raster conversion, can be 
developed from the results of Tanninen and Samet [1986 
] and Atkinson, etal. [1985]. Another is algorithm between 
TEN and NURBSs which is similar to the generation of 
TIN from contours and contours from TIN. The third is 
algorithms between Octree and NURBSs. The algorithm 
from NURBSs to Octree can be formed from Fisher and 
Wales [1992]. The algorithm from Octree to NURBSs is 
realized firstly interpolating subsurface points from 
Octree, then establishing NURBSs parametric 
coordinates. Some algorithms of these have been 
realized in author's research work. 
5. APPLICATION AND CONCLUSION 
An application of 3-D GIS is being carried out by authors 
in WTUSM, CHINA. Test area is a 9 km X km coal field, in 
which about 100 drillings are spaced. There have three 
coal layers and several rock layers. Test data include 
sampling data of drillings, information of earth surface, 
location of drillings and position of faults. Research works 
involved establishment of 3-D model of test area by use 
of different data structures, 3-D visualization and some 
spatial analysises for different geology constructions such 
as coal layer and fault. A HP Workstation, Starbase 
graphic library and C language are used. 
In 3-D GIS, objects are very complex. For example, in 
Mine Information System there have ore body, gallery, 
shaft, earth surface and building, etc. None of the 
structures has ability to represent all objects well. Also, 
each structure has it own advantages in spatial operation 
and analysis such as raster is convenient for Boolean 
operation and vector is easy for geometric transformation. 
Hybrid data structure may be a better means to balance 
different requirements. In this paper authors pay more 
attention in hybrid data structure and integration of data 
structures in 3-D GIS. A hybrid data structure based on 
Octree and TEN is presented and a concept of 3-D GIS is 
introduced, and some related issues such as data 
organization, formation of data structure, data conversion 
and application are discussed. These works are 
contributions to the development of 3-D GIS. 
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