Study Of Real-Time Rendering In Complex Virtual Environment

Virtual Reality has been widely used in the fields such as flying simulation,interactive GIS,virtual touring,digital earth,information visualization,architecture walkthrough,etc. These application need not only realism complex Virtual Environment,but require the user can interact with the virtual scene at interaction frame rate. As long as meeting the real-time rendering,the user can feel the virtual environment is the same as the real world and immerse into the environment. However,Virtual reality communities and other visualizations have always faced the problem that their "desirable" visualization dataset sizes are one or more orders of magnitude larger than what the hardware can display at interactive rates. Thus we need resolve the problem by attempts to bridge the gap between the desired and the actual hardware performance,through algorithmic and software techniques. The most critical problem in VR is real-time rendering the complex Virtual Environment.The general virtual environment is composed of terrain,clouds,tree,forest and other complex geometry models. In this dissertation,we mainly research the real-time rendering of complex virtual environment which includes the real-time terrain rendering,real-time modeling,3D complex model simplification and acceleration techniques. We have gained some research results and realize these innovation to actual virtual scene rendering which can meet the requirement of interaction without clearly degenerating image quality.The main research results include:1. In this dissertation,we present an algorithm of view-dependent continuous level of detail terrain simplification and 3D clouds rendering based-on fractal. The terrain mesh generated by using previous random mid-point displacement is usually uniform. When the viewpoint is far away from the terrain block,you need not rendering the terrain with higher detail. We introduce the method of LOD simplification into fractal terrain rendering to generate multiresolution terrain and reduce the triangles rendered and improve the performance. And,we have successfully used this method to render three dimensions clouds. You can dynamically simulate the motion of clouds by using the random function and adjust the random displacement of terrain height value and fractal dimension to change the terrain silhouette and surface roughness. In order to resolve the clear terrain crease,we use vertex interpolation to smooth the height value and enhance the coherence between of vertexes.2. In this dissertation,we present an algorithm of view-dependent LOD three dimension fractal trees. The tree modeling is based-on fractal iterated. The algorithm can simulate different kinds of trees and provides a method of leaf simulation that is named plant shape construction. The algorithm has many advantages such as simple,easy to carry out,a little calculation and a good real-time characteristic. By controlling the iterated levels,you can automatically generate LOD trees and select the appropriate LOD model to render according to the viewpoint changing.3. In this dissertation,we present a new algorithm of polygon simplification togenerate different LOD based on the edge collapse. When calculating the cost ofedge collapse, we consider the influence of edge length and surface curvature. And,the position of the new vertex is selected from the veYtexes of the edge collapsed,this can not only preserve the initial model shaPe, but also reduce the calculation ofCPU and meet real-time rendering of Virtual Environment. Vertex morphing is usedto smooth LOD model to reduce the popping between different LOD transition. Wehave enhanced the polygon data structure to implement the algorithm and proved theefficiency of the algorithm by a typical example.4. In this disseYtation, we present a new algorithm of View-Dependentmultiresolution terrain simplification based on adaPtive quadtrees. Especially, wediscuss these main problems in multiresolotion terrain rendering such as levels ofdetail mesh generation, ved...