where \(a\) and \(b\) are the lengths of the semi-axes perpendicular to the rotation axis, and \(n\) and \(n^{\prime}\) are the "numbers of principal curvature" that terminate semi-axes \(a\) and \(b\...where \(a\) and \(b\) are the lengths of the semi-axes perpendicular to the rotation axis, and \(n\) and \(n^{\prime}\) are the "numbers of principal curvature" that terminate semi-axes \(a\) and \(b\), respectively ( \(n, n^{\prime}=0\) for a flat surface, 1 for a cylindrical surface, or 2 for a spherical surface).
