Well, you know the normal vector.
那么当然知道它的法向量。
那么法向量又是什么呢？
Why would we ever know a normal vector?
为什么我们会知道法向量？
Why else would you know a normal vector?
还有什么原因你会知道法向量？
The normal vector will just be the gradient.
法向量就是梯度向量。
But you can also just stay with a normal vector.
但是你也可以继续只用法向量的。
And that is, in general, not a unit normal vector.
这通常不是一个单位法向量。
Now, let's multiply that by the unit normal vector.
现在用单位法向量乘以那个。
Now take your disk with its normal vector sticking up.
现在我们拿这个法向量向上的圆盘。
All right, it has the same normal vector as the surface.
它和曲面有相同的法向量。
And so the normal vector is going towardS what is up for me.
所以法向量指向我的上方。
This vector is called a normal vector or normal for short.
这一向量就称为法线向量或简称为法线。
The normal vector is just sticking straight up or straight down.
从而法向量的方向是竖直向上或向下的。
It can be a normal vector of any length you want to the surfaces.
它可以是曲面上想要的任意长度的法向量。
And then get this equation for the plane using the normal vector.
然后利用法向量得出切平面的方程。
This is a normal vector of the same length as n, well, up to sign.
这是与N长度相同的法向量，只是符号不定。
Let me re-explain quickly how I got a normal vector for the cylinder.
我来再次解释一下如何得出这个圆柱面的法向量。
Each edge point has a normal vector pointing in the direction perpendicular to the edge.
每个边缘点具有正常矢量指向在垂直的方向上的边缘。
Each edge point has a normal vector pointing in the direction perpendicular to the edge.
每个边缘点具有正常矢量指向在垂直的方向上的边缘。
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