基于Geometry Clipmap的三维地形可视化研究

摘要

With the wide use of digital technology and the growing popularisation of informatisation,the importance of realising 3D terrain visualisation becomes increasingly clearer.But the normal PC memory capacities cannot accommodate massive geometric and texture data.To solve this problem and to guarantee the efficiency of drawing,we adopted the Geometry Clipmap algorithm to draw the terrain,made the full use of GPU to improve the efficiency of drawing,and obtained elevation values of every vertex through vertex textures.Meanwhile,we simplified the organisation mode of triangle strips,used the simplified view frustum clipping method and the dynamic rendering layers number determination method to reduce the number of vertexes to be drawn.Based on the structure of specific layer,we came up with the new method (binary positioning method)of data update to reduce data updating amount of each frame during the motion of viewpoint.Experimental results showed that the new algorithm completed the large-scale terrain rendering by using a little memory,and got a higher frame numbers with smooth roam,guaranteed the realistic display of terrain,and was able to meet the demand of real-time visualisation of large-scale terrain.%随着数字科技的广泛应用和信息化普及的逐渐深入，实现地形的三维可视化的重要性日渐彰显。但目前的普通PC内存容量无法容纳海量的几何数据和纹理数据。为解决这个问题并提高绘制的效率，采用Geometry Clipmap算法绘制地形，充分利用GPU以提高绘制效率，通过顶点纹理获取各顶点高程值。同时，简化了三角形条带的组织方式，使用简化的视锥体裁剪方法和动态确定绘制层数方法减少需要绘制的顶点数。根据特定层结构，提出数据更新的新方法（二进制定位法）减少视点移动时各帧的数据更新量。实验结果表明，该方法使用很少的内存完成大规模地形绘制，且取得了较高的帧率，漫游流畅，保证了地形的真实感，能满足大规模地形实时可视化的要求。