Patent ID: 7917342

Claim:
A computer aided design system comprising: a point sequence information extraction device which extracts a plurality of point sequences on a curved surface; a dividing device which generates a curved surface from the point sequences using another computer aided design system, and divides the curved surface into a mesh having a predetermined number of mesh points; a first fundamental form computing device for computing coefficients of a first fundamental form at a mesh point of the mesh, the coefficients of the first fundamental form being defined at the mesh point by first-order differential values of the mesh point; a second fundamental form computing device for computing coefficients of a second fundamental form at the mesh point, the coefficients of the second fundamental form being defined at the mesh point by a product of second-order differential values of the mesh point and a normal vector of the mesh at the mesh point; a memory device which stores the point sequence information, the coefficients of the first fundamental form and the coefficients of the second fundamental form; a principal curvature computing device which computes a principal curvature of the mesh point based on the coefficients of the first fundamental form and the coefficients of the second fundamental form; a line of curvature computing device which computes a line of curvature showing a principal direction of the mesh based on the principal curvature; a feature point/feature line analyzing device which extracts a point or a line which becomes a reference point or a reference line, respectively, of a transformation defined by changing patterns of one or more feature quantities among five feature quantities showing features of the curved surface, the five feature quantities comprising a Gaussian curvature and a mean curvature computed based on the principal curvature, the principal direction, the line of curvature, and the coefficients of the first fundamental form and the coefficients of the second fundamental form; and a girth length computing device which computes a girth length based on a curvature computed from the coefficients of the first fundamental form and the coefficients of the second fundamental form.