数字地球中实时地形晕渲的实现方法

通过使用法线贴图的模式,不增加地面网格数的前提下,在三维数字地球仿真系统中实现了对全球地形的高精度实时晕眩效果的地形浏览.首先通过对高程数据进行分层分块处理,制作级地块法线贴图,再通过绘图芯片用可程序化像素着色器流程计算法线贴图的光照效果,最后将纹理贴到对应的分层三维地形网格上.根据光源的入射方向、色调、饱和度及亮度,计算中考虑了顶点的环境光、漫反射光、镜面反射光,在低地形网格数的前提下,实现了如高精度地形网格般的明显光影变化. 

Method of realtime hill-shading in digital earth system

Hill-shading terrain effects, which are high precision and real-time dynamic, were achieved on global terrain in the digital earth simulation system developed. It was realized by using the normal map mode without increasing the number of terrain grid. The elevation data was processed to level of detail chunked and create normal map of all levels by calculating normal. Lighting effects of normal map were calculated by pixel shader and the texture was pasted onto corresponding layered terrain meshes. By the direction of incidence of the light source's incidence direction, hue, saturation and brightness, the vertex's ambient light, diffuse light and specular light was calculated. At low-precision terrain grid, obvious changes effect of light and shadow as high-precision terrain grid was reached.