说明：  表面法线是几何体表面的重要属性，在很多领域都有大量应用，例如：在进行光照渲染时产生符合可视习惯的效果时需要表面法线信息才能正常进行，对于一个已知的几何体表面，根据垂直于点表面的矢量，因此推断表面某一点的法线方向通常比较简单。
(The surface geometry of the surface normal is an important property, has a large number of applications in many fields, such as: generating illumination during the time required to render a visual effect in line with the surface normal vector information customary to work correctly, for a given geometry surface, according to the surface perpendicular to the vector points, and therefore infer the surface normal direction of a point usually simple.)