Examples and Conclusions
Based on the above presented algorithms and methods, we have developed a system for 3D geological data modeling and visualization in Japan. Figure 3 shows the different views of 3D geographic and geological data with their mage textures on the ground surface. Figure 4 shows a part of enlarged view ground surface with DEM, contour maps and air photos. Figure 5 shows result of under ground geological structures with overlapped map layers. In this figure we can see geological subsurface, under-ground water structures, and designed highways. Figure 6 shows the results of vertical geological cut planes with topographic maps and DEM.

Figure 3. The different views of 3D geospatial data with their mage textures.



Figure 4. An enlarged view ground surface with DEM, contour maps and air photos.



Figure 5. The result of under ground geological structures with overlapped map layers.



Figure 6. The results of vertical geological cut planes with topographic maps and DEM.
From above approaches and experiments we can find that the presented hybrid 3D GIS model based on DTT is a very useful tool not only for 3D geospatial data management and visualization, but also for data manipulation and sophisticated analysis. Integration of different kinds of geospatial data, such as the data from geology, urban planing, environmental monitoring and archeology, will extent wide application fields of 3D GIS.

For our further researches, the algorithms for extraction and modeling of complicated 3D geospatial objects in their detail structures by using airborne laser range scanning data will be investigated. For the application of 3D GIS, reconstruction and management of 3D geospatial objects around highway for Intelligent Transformation System (ITS) is mostly interested.

Acknowledgments
The authors wish especially to thank Dr. R. Imamura and Dr. T. Doihara for their considerable helps and supports of this research project. The first author also want to thank Asia Air Survey Co. ltd., Japan for getting the permission to use the testing geological data.

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