| This paper explores multi-resolution modeling and algorithms implementation of the large-scale terrain environment, and designs and establishes a prototype system of virtual terrain environment system. Two case studies of Yuanlang and Da -Yu-Shan regions, Hong Kong are carried out. The principal content in this thesis is as follows.â—† Study status and related techniques of virtual terrain environments are discussed in terms of 3DGIS(Three-Dimensional Geographic Information System), the digital earth, the virtual reality, and so on. Furthermore, the paper studies the generation and rendering of models at multiple level of detail (LOD) and visibility-based simplification used for real-time graphics rendering in large-scale virtual terrain environments.â—† Different terrain rendering methods are put forward integrated with characteristics of landform. Several terrain representation modes and applications in proper environments are addressed.â—† The 'pyramid' data structure is presented according to the characteristics of VRML (Virtual Reality Modeling Language). The quad-tree automatic simplification technique is used for that terrain in different "pyramid" levels takes on different resolution, and terrain in the same level has multi-resolution.In order to solve geometry-gaps, the author studies and compares two ways: pattern of restricted quad-tree and mark points and pattern of changing connectivity of vertices for higher resolution.â—† Based on VRML, a distributed virtual terrain environment system is designed which has a thin-client/thick-server network structure, and a prototype system is established.In the two case studies, experimental results show that the simplification algorithm is practical and efficient. A compressing optimization method of VRML terrain data files is also studied in this paper. |
