In order to solve problems of heavy rendering loads and unstable frame rates caused by huge data and rich details of large terrain in flight simulation, a terrain modeling method based on Tessellation was proposed. The key idea of the method is to build a view-dependent multi-resolution LOD structure of terrain based on geometry clipmaps. Firstly, several Tessellation control points, which are able to express structures and all states of geometry clipmaps by index groups, were generated in CPU and stored in vertex cache. Then, index points were generated in index cache by each level of geometry clipmaps according to Tessellation control points in vertex cache and transferred from CPU to GPU. Secondly, adaptive triangle patches were generated by GPU tessellation shader according to index points in GPU. In update phase of rendering cycle, states switching of geometry clipmaps was did by simply replacing index points in changing regions. Finally, ‘cracks’ caused by different resolutions between adjacent levels were eliminated by modifying outer tessellation level factor of shared edges between levels, which can generate triangle patches from inside to outside at shared edges of outer level corresponding to the inner level. The experimental results showed the proposed method can make full use of new features of the latest graphics cards. It is able to decrease data transmission from CPU to GPU while achieves the balance of rendering loads, and improves the rendering efficiency and real-time frame rate stability during terrain navigation. The proposed method of crack eliminating is simple and effective, which ensures the real degree of details of large terrain and meets the requirements of stable real-time terrain rendering in flight simulation.
