Topic summary
Surface normal
Extracted from the Wikipedia article Normal (geometry).
In three-dimensional space, a surface normal, or simply normal, to a surface at point P is a vector perpendicular to the tangent plane of the surface at P. The vector field of normal directions to a surface is known as Gauss map. The word "normal" is also used as an adjective: a line normal to a plane, the normal component of a force, etc. The concept of normality generalizes to orthogonality (right angles).