Normal plane (geometry)

The normal section of a surface at a particular point is the curve produced by the intersection of that surface with a normal plane.

If the surface is bow or cylinder shaped, the maximum and the minimum of these curvatures are the principal curvatures.

If the surface is saddle shaped the maxima of both sides are the principal curvatures.

The product of the principal curvatures is the Gaussian curvature of the surface (negative for saddle shaped surfaces).

This differential geometry-related article is a stub.