The images are the exterior shells prior to feature creation of the final 3D models. Surface modeling is the most complex of the 3D world. In industrial design, model creation consists of solid and surface modeling. These examples consist of G1, G2, and G3 surface continuity. G2 is Class-A surface continuity. G2 continuity exists on surfaces in aerospace and the auto industry, these surfaces must meet aerodynamic requirements and they are the smoothest of the surfaces.