Study On The Theories And Methods Of Railway 3D Visual Design

The railway 3D visual design plays an important role in checking up the projects of railway and improving the quality of railway design ,because the key to implement railway 3D visual design is building 3D model of railway line landscape , The study on the methods of building 3D model of railway line landscape is of important academic meanings and practical values.In this paper, generating 3D digital terrain model by means of aerial survey data or manual survey data in the region railway will be constructed, utilizing plan , profile , cross section data and bridge, tunnel, railway bed data to create 3D railway line model and merging the two models to form a 3D model of railway line landscape are studied.Based on analyzing the algorithms of Delaunay triangulation creation in domestic and abroad, in view of the situation of building DTM and the need of realizing railway 3D visual design , a divide-and-conquer algorithm to build DTM is presented , the algorithm use square grids to manage disordered points,to form triangular meshes in grids , DTM can be obtained by merging the triangular meshes . so that the work of sorting of the disordered points before building DTM is reduced greatly ; moreover,the algorithm utilize subarea to control the vertices of convex hull so that the range which support points locate in can be predefined when searching support points, the workload of searching support points can be reduced and the speed of merging two triangu-lations is raised.A method for inserting constrained boundaries in DTM based on studying on generating of constrained Delaunay triangulation is presented. First, searching for the diagonals which not intersecting with the constrained boundaries . Then using them to cut the influenced area, the method has the adventages of a plain principle and a fast speed.A method of utilizing plan, profile , cross section data and digital terrain model to establish the 3D models of the main constructions of railway line and terrain model is presented. It describe the irregular entities surfaces by cutting them into regular entities surfaces so that it is simple and can raise the speed of drawing and display of the entities.the method is not only suit for single track railway line but also suit for double track railway line.Merging terrain 3D model and railway line 3D model to build 3D model of railway line landscape is the core of implementing railway 3D visual design , the key of merging the two models is hiding the ground which the railway line to be constructed,the problem is studied in this paper and a divide-and-conquer method is presented. First, generating a regular quadrangular mesh by means of DEM data . Then finding out the regions that railway beds locate in and cuting the regions into grids, if the boundaries in a grid exactly blanket the grid then delete the grid, if the grid contains the boundaries then forming two triangles using the four vertices of the grid, finding out the points where the boundaries and the triangles intersect, inserting the points and the vertices of the boundaries into the existed triangular mesh to form a new triangular mesh . At last deleting the triangles which locate into the boundaries and the ground is hided, moreover.the problem of merging two railway beds which are interrelated and terrain surface is solved by using separate-and-intersect method in the segment where the railway vary from a double track railway integral bed to two beds of single track railway or two beds of single track railway to a double track railway integral bed.Based on the mathematical model presented in this paper.complete developing railway 3D visual design system with object Oriented programming . The correctness is proved by using the software to have made the 3D landscape model and animation of Xi'an-Nanjing railway, Xi'an-Yan'an railway, SuiLing-ChongQing railway, etc; at the meantime ,the practicability and adaptability is discussed.