2) Gaussian Curvature: Gaussian curvature (K) is an intrinsic measure and simply the product of the principal curvatures as K = κ 1 κ 2 for a given point on a surface, equivalent to the determinant of local Hessian matrix H e . Note that K is unchanged even by bending the surface without stretching it, meaning that the Gaussian curvature is independent of the choice of unit normal and it gives three types of classified local shapes: elliptic shape (K > 0), hyperbolic shape (K < 0), parabolic shape (K = 0) with one of the κ is equal to zero, planar shape (K = 0) with both κ are equal to zero. Gaussian curvature is translation and rotation invariant, but not scale invariant.