视锥体裁减的一个例子，通过对视锥体和roam地形数据的相交检测来预先排除在视景体外的地形数据，加快显示速度。demo形象的演示了裁减的实现效果，代码也有详细注释，适合当作教程学习。-Cone cuts as an example, by Cone and roam, as the terrain data in advance of the intersection tests to rule out the possibility in view of the terrain data in