The Research And Realization Of Modelling 3D GIS

3D GIS is a key technology for developing new generation GIS.The thesis first promotes based Object Oriented Modeling method-Aggregating & Deriving Mothod.Its main idea is dividing model into base model and applied model. The base model consists of three prototypes-point, line and triangle-and derived entities that aggregated from the prototypes, which applies to different situation; the applied model is derived from the base model by adding some additional condition. The characteristics of the modeling method are avoiding data redundancies, topological relation is clear and having more flexibility. Then, the thesis validates its feasibility and correctness from two aspects-terrain and building.For 3D entity, the main thing is that how to divide, organize, store and search. The thesis regards a building as an object; divide the building into a roof and metopes, divided in this way and come down to three prototypes. The data storage is based on RDS, design spatial database under the direction of object oriented concept and realize object storage.For real 3D terrain, after analyzing exiting algorithms and combining the characters of the modeling method, the author improves D-Triangle algorithm. The traditional algorithm needs to construct a protruding polygon including all discrete points. On the one hand, the polygon construct difficultly, on the other hand, the base model dosen't exist polygon. So the thesis replaces take the polygon place with a super-triangle. When insert other discrete points into the super-triangle, the author makes full use of D-Triangle's characters. In this way, it dose not reduce the optimizing step, but alse enhance the algorithm efficiency. The improving algorithm is correct by experiment test.As the respect of visual of terrain, because the limit computer capability, it is hard to visualize large, vast data and move it freely and fastly. So the thesis puts forward a based LOD square-tree terrain algorithm. It uses four-tree to divide and unite. At the same time it also gives the data segment and instructing strategy. At last it realizes four level LOD models.In the end, the thesis collects some data from existing electro-map and some blueprints of Jiangsu University and successfully realize 3D model of digital campus of Jiangsu University by this modeling method.