Research On Real-time Rendering Of Multi-resolution Terrain Features

High performance real-time rendering of terrain features using multi-resolutionmethods and techniques is not only an important requirement of many applications, butalso a key technology in computer graphics and terrain visualization. The basic idea ofmulti-resolution is to choose and use data with appropriate resolution dynamicallyaccording to view point and requirement of visual consistency. The goal is to achievebest visual effect and real-time performance. Therefore, the theory is based onquantitative mathematical relation between rendering performance, visual effect,resolution, data amount and dynamic resolution switching method.According to the principle of multi-resolution and requirement of real-timerendering of point, linear and area features, main factors that affect renderingperformance are analyzed. Different multi-resolution models and dynamic resolutionswitching methods are proposed as the characteristics of different terrain features areconsidered.As the layered trait and spatial distribution of point features are regarded,multi-resolution data organization based on best spatial partition and resolutionswitching based on the height of view point are suggested. The quantitative relationbetween performance, data amount and partition size are also deduced. The bestpartition size can be decided through experiments to realize high performance andeffect.For linear features, the visual error is examined with respect to view point andworld coordinate and is used as the criterion to construct multi-resolution modelsthrough simplification of linear feature vertexes. Based on the fact that the averagevertex rendering time is related with the total number of vertexes and the graphic system,a geometric rendering method is advocated through virtual connection with best linelength. The best line length is selected through experiments to improve the renderingperformance of large scale linear features. The result shows that it is still sufficient toget real-time rendering performance even for features with more than one millionvertexes.For area features that require continuous and smooth outlines, a multi-resolutionmethod through approximation of curves with variable number of vertexes is putforward using either second order or third order Bézier curves. The formulae ofcomputing control points are presented and the multi-resolution rendering algorithm isdesigned and implemented based on computational characteristics of Bézier curves andestimation formula of traverse error for vertex approximation. The conclusion is torecommend the third order Bézier curves when the chances are same.Through theoretical analysis, program design and experiment, it is proved that multi-resolution methods are feasible, correct and effective. The future trend of highperformance terrain rendering is to harness graphic processing unit and parallelcomputing as well as multi-resolution techniques.