Visual Research For3D Terrain Based On Buffer And Laplace Mesh Simplification

Nowadays, the modeling and visualization of3D terrain is of great importance inglobal information system. There are a lot of software related with3D data process andmanagement in our society, but they are not specially designed for3D terrain, so the abilityto manage the large scale data of terrain and render the terrain timely is quite poor. Basedon this, the paper is committed to design a visual system of3D terrain, which realizes thereal time rendering of real3D terrain. The system enables the user to conduct spatialanalysis and interact with it.The research mainly includes: the division of3D terrain, loading and dispatch of thesub-block, multiple buffer strategy, the mesh simplification based on the Laplace operator,GPU-CUDA parallel programming, and how to divide the program into models accordingto their functions.The paper introduces several methods to acquire data of3D terrain, and it selects DEMand DOM to depict the true terrain. Because the local area of terrain is always shown inrendering, the data of terrain is divided into sub-blocks. Then they are stored into Oracledatabase, which facilitate the access of the data. The quad tree structure is introduced toexpress the sub-block. Relying on the method of level of detail, the showing of3D terrainwith multiple solutions is realized.Given the view point and direction of sight, we can calculate the sub-blocks which areto be rendered. To diminish the frequency of reading the external storage, the multiplebuffer mechanism and data dispatching strategy are introduced. By calculating the priorityof the sub-blocks, we can tell the sub-block is loaded into memory or is substituted. Themultiple buffer mechanism and data dispatching strategy is realized separately, if thecircumstance is changed, we only need to change the data dispatching strategy. To diminishthe amount of data flown into graphical pipeline, view-dependent frustum culling, back faceclipping and mesh simplication are performed. During the period of mesh simplication, weuse Laplace operator to calculate the sharp degree of the mesh point, which helps tocalculate view-dependent error. This method guarantee an low error with stable rate ofsimplication. The mechanism of negative feedback control is adopted to set the thresholdvalue of error. We add triangles when the fractures are occurred where the resolutions ofnodes of terrain is different. GPU-CUDA programming is introduced because theprevalence of GPU processor. The sub-blocks of terrain is treated as several CUDA flow, and each point is considered as an independent thread. Because several calculations areexecuted simultaneously, the time of computing is reduced sharply.Several modes are adopted to display the terrain, such as hypsometric tint diagram inwhich points with different heights are paints with correspondent colors. By settinglighting, material and texture, the shade effect and realistic surface of terrain is realized. Toserialize the model of terrain processed by static simplication, the method of optimizing theconfiguration of triangle is introduced, which increases the hit rate of point buffer in visualmemory.To better perform the interaction and spatial analysis, perspective projection andorthogonal projection are provided. Mouse and keyboard are utilized to control the viewpoint and direction of sight. Through clicking the window,3D coordinate are extracted, thenthe distance of the points are calculated. In the mode of orthogonal projection, functions ofzoom and translation are realized, which help to observe local area.In the end, the paper indicates how to divide the program into models, which include:display model of OpenGL, OCI model of database, model of geometric object, and modelof terrain. Several classes is divided inside the model. Take the model of terrain as anexample, there are class of buffer mechanism, class of data dispatching strategy, class ofassembling the basic primitives into geometric object. These classes have clear interfaces ofinput and output. The feature of inheritance and polymorphism is utilized to extendfunctions of the program, which meet the ever-changing requirement. MFC mechanism isadopted as the main framework, function of serialization and mode of document-view areapplied. By operating the database, several projects of terrain can be managed.Above all, database of Oracle is utilized to access the data. To handle the large amountof data, several methods such as dividing the terrain into sub-blocks, multiple buffermechanism, clipping and culling are adopted. To simplify the mesh efficiently, Laplaceoperator is introduced to calculate viewpoint dependent error. The detailed framework isgiven in the end of the paper. The visual system of3D terrain has a broad prospective inpractice.