求解二維和三維法向量的方法

二維曲線法向量的求解示例：

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:

三維三角面片頂點法向量的求解：頂點相鄰各個三角面片單位法向量的疊加。

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:

---

    
 
	v = normalised(sum(v12, v23, v34, v41))
	
	where
	
		vij = normalised(vi x vj) // normalised cross product