| 3D GIS is one of the most popular trends, it can describe the objective world more visually and vividly. As the important area of human living, urban planning and management could be even more in the spotlight. Recently, with the continuous improvement of digital city theory, the3D modeling and visualization of city has become a hotspot in research of GIS.At present, the development of the digital city is still in the primary stage, Most research focused on the visualization of city, but there are still many problems in areas such as rapid construction of3D model, storage of massive data and acquiring of real-time3D spatial data. The article makes a thorough research on rapid construction of3D model, and analyses more often used3D spatial data model and3D modeling software, considering the modeling rate, complexity, the scene of reality and the seamless integration of terrain and buildings, the appropriate models to construct terrain and buildings are put into study with cases respectively.In order to achieve terrain modeling quickly, an effectively combined algorithm of generating TIN based on the quad-tree structured index is proposed in this paper. Using this algorithm, discrete points are firstly divided by quad-tree based on their position and density. Then using incremental insertion algorithm, triangulation is built, with quadrilateral boundary of each leaf node as convex hull. Finally, the four sub-nodes with the same parent are bottom-up merged with vertex combined approach to generate Delaunay triangulation. The results of experiment show that the algorithm has a low time complexity and effectively improves the efficiency of generating TIN.The building is an important part of land features. In order to achieve building modeling quickly, a pattern combined with CSG model and SketchUp software is proposed. For constructing regular buildings using CSG model, first, we establish basic model library of CSG block element, then select appropriate CSG block elements according to the shape of the buildings, and finally using boolean operation to combine these block elements into a continuous building. We construct irregular buildings with SketchUp software. first, we map building models using tools including chain the path, push-and-pull, scaling for stretch, etc., then modify the building models and texture mapping, finally convert them to3ds models.Constrained Delaunay TIN(CD-TIN) can be used to integrate buildings and terrain. First we use TIN to construct terrain model, then extract the underside boundary polygon of buildings, finally insert these polygon as constraint line into terrain triangular irregular network.Based on the modeling method mentioned above, An experimental system of3D modeling and visualization of city are designed to test the model and algorithm with experiment using the data of Beijing. |
