Abstract: A two levels of detail terrain is presented in this paper.During the lower Level Of Detailed（LOD） terrain，we simply render the whole terrain using ROAM mesh independent of view.During the high LOD terrain，we render the fluctuant detail of terrain’s height using symmetrical mesh along view center.We control upper LOD terrain’s range by adjusting projective area proportion between upper LOD terrain and the whole terrain.Transitional area of the two level terrain is pushed away from the view.Based on the resolution difference between lower level and upper level，we calculate the transitional area’s width，and ensure the two LOD terrain’s smooth transition by rendering the areal color based on image special Per-Pixel displacement texture method.

Key words: two levels of detail, transitional area, terrain mesh

摘要： 提出了一种双层次细节地表模型的快速绘制算法。建立了双层次细节地表模型，在模型的低层次细节中，采用了视无关的ROAM网格粗略地表示整个地形地貌；在高层次细节中，借助以视点为中心的均匀网格描述地形高度起伏的细节。通过调节高层细节与整个地形投影面积的比例，控制高层次细节覆盖范围，把两层模型的过渡区域推向离视点较远的位置。过渡区域采用了基于图像空间的逐像素纹理混合与偏移方法生成该区域的颜色，保证双层次细节的平滑过渡。实验证明，该方法在保持逼真视觉效果的同时，能够较大规模地提高三维地形绘制速度。

关键词: 双层次细节, 过渡带, 地形网格