Research On Terrain And Landform Modeling For Virtual Geographic Environments

Visualization of large scale terrain is playing a key role in the study of virtual geographic environments. This thesis focuses on real-time display of large scale terrain and the representation of realistic terrain and landform . The principal contents are as follows:Some fundamental strategies and related techniques for the real-time rendering of large scale terrain are investigated. The author describes and compares several well known algorithms for real-time rendering of large scale terrain.A quadtree-based algorithm for real-time continuous level of detail reduction is designed. Geometrical terrain data is dynamically divided, and top-down refinement is used in this algorithm. An error criterion for terrain simplification is presented. In order to avoid cracks, the restricted quadtree way is used and the connectivity of vertices of higher resolution node is changed.Another algorithm for real-time terrain rendering using geometrical MipMapping is presented. Several key problems such as data organization, frustum culling, LOD level choosing, cracks avoiding and triangulation are discussed. The algorithm is efficient in computation and memory and requires low-end 3-D graphics card.Some methods for generation of several realistic 3-D models such as dam, tree and terrace in the watershed are discussed.A prototype system is developed using C++ and OpenGL API. Experiments show that the two algorithms presented in this thesis are efficient and can support the real-time navigation for large scale terrain.