Editing Curvature (section)

====Principal curvature====
[[File:Minimal surface curvature planes-en.svg|thumb|300px|right|[[Saddle surface]] with normal planes in directions of principal curvatures]]
{{Main|Principal curvature}}
All curves on the surface with the same tangent vector at a given point will have the same normal curvature, which is the same as the curvature of the curve obtained by intersecting the surface with the plane containing {{math|'''T'''}} and {{math|'''u'''}}. Taking all possible tangent vectors, the maximum and minimum values of the normal curvature at a point are called the '''principal curvatures''', {{math|''k''<sub>1</sub>}} and {{math|''k''<sub>2</sub>}}, and the directions of the corresponding tangent vectors are called '''principal normal directions'''.