The problem of normal vector The normal vector of space surface, add a negative sign before the vector, or the normal vector of the point? How to judge the positive and negative direction?

The problem of normal vector The normal vector of space surface, add a negative sign before the vector, or the normal vector of the point? How to judge the positive and negative direction?

The plus minus sign should still be a normal vector. It's related to the orientation of the surface. If we study the orientable surface, for example, the parameter expression of your surface is p (U, V), P is the mapping from RXR to R3, and the partial differential of P with respect to u (a vector) is generally linearly independent of the partial differential of P with respect to V (another vector)