Normal refers to the 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.

Every curve has a tangent at this point, that is, countless tangents can be made at this point, which proves that these tangents are all in a plane, and this plane is the tangent plane. In addition, the straight line passing through this point perpendicular to the tangent plane is the normal, which is unique. So a point on the surface has a tangent plane and a normal direction.

Extended data:

1, the normal is used to describe the direction of the surface, and the direction of the surface is very important. For example, if you paste a picture on a surface, it's like pasting a word on glass. On the reverse side, the word will be reversed, so the surface normal is necessary. In addition, the inconsistent direction will also lead to the inability to weld, UV flip and so on. 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.

2. The normal of the curve is a straight line perpendicular to the tangent of a point on the curve, and the normal of a point on the surface refers to a straight line (that is, a vector) passing through the point and perpendicular to the tangent plane of the point. The line perpendicular to the mirror through the incident point is called the normal. 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.

3. For a solid surface, the normal is directional: generally speaking, what points from the inside of the 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.

4. Application of normals in 3D software: The positive and negative normals will have an impact when UV pastes materials. If the normal is negative, the material you paste will also look back. 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.