Research On The 3d Real-time Interactive Computer Aided Design System Of Highway And Its Kernel Arithmetic

The visualization of three-dimensional (3D) road is an important component of the road Computer Aided Design, which can generate a realistic 3D scene of road and terrain by combining a traditional two-dimensional (2D) flat, vertical and horizontal design with 3D visualization technology. It takes an important role in the improvement of road design, landscape design quality, and the evaluation of route safety.This thesis applies synthetically those theories and technologies of computer graphics, computational geometry and geometrical modeling, interactive, virtual reality etc, to research thoroughly and carefully on several critical technology of computer aided alignment design, such as a based on mass TIN rapid generation algorithm of digital terrain model, a seamless integration algorithm of several models, a continuous LOD algorithm of TIN terrain model. The chief research contents and achievements could be summarized as follows:1) Based on the theories of delaunay triangulation, the algorithm for fast creating irregular triangulation net (a compound algorithm based on horizontal expansion and divide-and-conquer algorithm for constructing delaunay triangulation). The algorithm is mainly based on divide-and-conquer and horizontal expansion algorithms, it divides a set of points into several grid tiles, and then construct subnet in each grid tile by horizontal expansion method. Finally, these subnets are recursively merged into a whole delaunay terrain triangulation model. The algorithm is simpler ideas, more efficient, more economical memory, which is more suitable for mass configuration of TIN terrain model.2) In the aspect of seamless integration algorithm of road model and TIN terrain model, considering the weakness of the traditional model semless integration algorithm, this paper presents an improved algorithm. The process is changed to a constrained delaunay triangulation by the proposed based on PSLG constrained delaunay triangulation method, and the optimized algorithms of embedding the constrained edges and swallowing the internal triangles. The new algorithm can improves the integrate speed, avoids the"hanging side"problem, and completely solve locality situation cause by concave polygon.3) In the aspect of the continuous LOD algorithm of TIN terrain model, this paper presents an edge collapse algorithm based on the weighted average vertex degree, in order to improve the efficiency of the terrain model simplification. During generating the LOD model, we divide the terrain into some blocks with grid lines to avoid the influence of the narrow triangles, and use progressive mesh algorithm to generate the LOD model of terrain block. When dispatching the LOD model, we use an effective method to determine the visibility of terrain block and dispatching LOD model method based on viewpoint, which realize the terrain continue multi-resolution rendering.Finally, the paper describes the system flow and experimental results in the real-time 3D visualization of the highway interactive and aided design system. And the above algorithm was verified in the system. The experimental results show that the correctness of the algorithms, and they are able to meet the need of the road 3D visualization, and the desired research objectives can be achieved ultimately.