二维曲线法向量的求解示例：
Here's an example using an analytic curve of y = x^2
x = 0: 0.1: 1; y = x.*x; dy = gradient(y); dx = gradient(x); quiver(x,y,-dy,dx) hold on; plot( x, y)which gives:
三维三角面片顶点法向量的求解：顶点相邻各个三角面片单位法向量的叠加。
http://www.lighthouse3d.com/opengl/terrain/index.php3?normals
The normal at a vertex should be computed as the normalised sum of all the unit length normals for each face the vertex shares. Consider the following image:
In the above image, v represents the normal at the center vertex. Each vij represents a normal for each face that shares the center vertex. So for instance v12 is the unit lenght normal for the bottom right face.
The vertex normal v is computed as the normalised sum of all vij vectors:
