现在在上方的曲面上，有一个平行四边形。

Now, above that I will have a parallelogram on my surface.

youdao

在曲面上做一些网格，你会看到一个网上的每一小块儿，都是小的平行四边形，我们要弄清楚它的面积和法向量是什么。

You will get some sort of mesh grid on your surface and you will look at a little parallelogram that is an elementary piece of that mesh and figure out what is its area and normal vector.

youdao

三角化曲面上的网格顶点和网格边被抽象为质点-弹簧模型，用来控制网格形状。

Vertices and edges on the triangulated surface are abstracted into a mass-spring model which is used to control the shape of triangles.

youdao