但是事实上它就是，如果你考虑一下的话，就是在给定点上的，最好的近似曲面的平面。

But, it's really, if you think about it, you will see it's really the plane that's approximating the surface in the best way that you can at this given point.

youdao

这就是切平面的，或者说这个曲面的法向量。

OK, and that's going to be the normal vector to the surface or to the tangent plane.

youdao

我这就要将曲面分解成小平面了。

I am going to decompose my surface into very small flat pieces.

youdao