3D Visualization Of Railway Roadbed In SuperMap Environment

Most traditional achievements in railway surveying and designing are 2D topographic map, but 3D ones are expressed through CAD system. Designers are unable to integrate survey with design. Application of GIS in railway surveying and designing map not only integrates data gaining, applying and processing, but also realizes multidimensional and dynamic displaying. So, the research on 3D visualization of railway in GIS environment has very important realistic significance.In respect of the technology and method of 3D modeling for railway, the key to realize 3D visualization is to establish roadbed 3D model and integrate roadbed 3D model with terrain 3D model. The major study contents in this paper can be summarized as follows.(1) The main methods of establishing roadbed 3D model, such as triangular irregular networks model, Coons surface model and solid model, are described in detail, and the advantages and the disadvantages of each method are pointed out.(2) Based on studying the merge of roadbed 3D model and terrain 3Dmodel in GIS environment, a method of establishing the whole 3D model by using spatial overlay analysis technology of GIS has been presented in this paper. Firstly, the closed polygon is made by connecting the vertices of roadbed boundaries according to certain rules. The area layer of roadbed is established on the basis of the closed polygon, and the point layer of terrain is generated with the original terrain points. Then, the original terrain points in roadbed area layers are deleted by spatial overlay analysis of point layer and area layer in GIS environment, and a new point layer of terrain is generated by the remaining original terrain points. Finally, a new point set is generated by merging the design points of roadbed and the points of the new terrain, and the new point set is converted to be the triangular irregular networks model with GIS control. So the 3D whole model whose appearance and inner topological relationship are both integrated is created successfully.(3) With SuperMap Objects5.2 which is a development tool of GIS based on COM technology developed by SuperMap GIS Technologies, Inc. as the platform and Visual Basic 6.0 which is the visual tool published by Microsoft Company as the developing tool, a railway roadbed 3D visualization system is developed. The system can generate quickly the whole 3D model of roadbed and terrain, realize rendering of 3D scene, inquiry geodetic coordinates of whatever point in 3D scene, realize the function of roaming of line, utilizing horizontal, vertical, cross-section ground line data and digital terrain model. The software is proved applicable and efficient with the preliminary design data of Yan'anbei to Zichang segment in Xi'an-Yan'an Railway.