梯形没有体积!它是一个平面图形!
Most of the two-dimensional models that manage topology are based on the planar graph theory.大多数操作拓扑结构的二维模型都是基于平面理论的。
By VRML, the users of the World Information Network can view spatial model, without being confined to planar graph, image.通过VRML,全球信息网的使用者可以观赏到立体空间的模型,而不限于二维空间的图形、影像。