Topological changes in the intersection of two isolines extracted from a function of two variables defined over 3D polygonal surfaces. The images on the left and right show the 3D polygonal surface M and range R2, respectively. Here, 16×16 resolution is employed to quantize the 2D range space, which is spanned by the two function values, i.e., the integral of geodesic distance from the shape center and surface curvature. (a) An ellipsoid surface and its corresponding joint contour net. (b) A spectacles polygonal surface and its corresponding joint contour net.