Research On Multi-resolution Representation And Visualization For Terrain Model In Virtual Reality

Terrain surface model has its important and wide-ranged application background in virtual reality. Presently, due to limited hardware capacity, for the large scope terrain, the real-time modeling and visualization is still big problem. The multi-resolution representation is a good way for creating of virtual terrain scene and the real-time rendering.In this dissertation, multi-resolution representation and visualization for terrain model are discussed. Based on survey of existing methods, some new algorithms and improvements are presented in detail here. Experimental results show that these methods are successful, practical and efficient, the dissertation consists the following parts:1) This paper advances terrain triangular mesh simplification arithmetic based on point group deletion. It designs accordingly data structure and simplification arithmetic. It advances also a new arithmetic what can generate and show the progressive mesh. The arithmetic records all information of point deletion on the simplification course and utilizes the relation between the point deletion and the quantity of the model's surfaces to build show fashion. It has realized a real time, continuous and multi-resolution show base on terrain TIN model.2) This paper advances a stepwise visual arithmetic by data-tiling. Firstly the arithmetic divides terrain TIN and builds LOD model database. Second the arithmetic confirms adaptively the required levels by user's standard. It has realized the LOD model's build and render what is viewpoint correlation real time and base on TIN model.3) The author puts forward a kind of topography error estimate method based on local-energy function, which makes multi-resolution topography model keeping lifelike in showing and better real-time computing capability. Relying on the relationship between point and point, the method of transmitting the error of point is adopted to solve the seam problem within the network of tree structure effectively. Based on this method the author puts forward a kind of new multi-resolution expression algorithm of self-adaptation on basis of quad tree, and realizes the multi-resolution expression and visualization correlating with viewing point of topographical RSG model.4) Texture mapping technology is used in visualizing the topography in this paper, propose, and the algorithm of quick topography rendering based on Mipmaps is put forward. Furthermore, the standard in detail level is analyzed. The author solves the seam phenomenon at the topographical tllm boundary by designing a kind of effective method and proposes one smooth algorithm of transition under model between different LOD models, trie author also realizes multi-resolution expression of massive topography and real-time visualization.5) The technology and method of cutting out of visual region on topography are researched, and several technologies and algorithms of improving and accelerating the cutting-out of visual region are discussed. The author proposes a quick algorithm of cutting visual region based on a level surround ball to accelerate the speed of topography visualization greatly.