The normal is a dotted line that is always perpendicular to the plane. In mathematical geometry, normal refers to a straight line on a plane perpendicular to the tangent of a curve at a certain point. Normal also applies to plane mirror reflection in physics.

For a solid surface, the normal has a direction: generally speaking, what points from the inside of a solid to the outside is the positive direction of the normal, and vice versa.

The normal direction of the surface normal is not unique; The normal in the opposite direction is also the surface normal. The normal of an oriented surface is usually determined according to the right-hand rule.

Extended data

Application of Normal in 3D Software

When pasting UV materials, the positive and negative normals will have an impact. If the normal is negative, the pasted material will also look backward.

The display and editing of normals in 3D software are almost the same, for example, in MAYA, that is:

Check the Face Normal under Polygon under the Display menu, and you can see that the Normal menu under Polygon panel is about normal, among which the most commonly used commands are Flip Normal and Clean ... The commands under Mesh menu can correct topological errors, and normal errors are one of them.

Baidu Encyclopedia-Normal