We investigate the usability of functional surface optimization for the design of free-form shapes. The optimal shape is subject to only a few constraints and is influenced largely by the choice of the energy functional. Among the many possible functionals that could be minimized, we focus on third-order functionals that measure curvature variation over the surface.

We provide a simple explanation of the third-order surface behavior and decompose the curvature-variation function into its Fourier components. We extract four geometrically intuitive, parameterization-independent parameters that completely define the third order shape at a surface point. We formulate third-order energy functionals as functions of these third-order shape parameters.

By computing the energy minimizers for a number of canonical input shapes, we provide a catalog of diverse functionals that span a reasonable domain of aesthetic styles. The functionals can be linearly combined to obtain new functionals with intermediate aesthetic styles. Our side-by-side tabular comparison of functionals helps to develop an intuition for the preferred aesthetic styles of the functionals and to predict the aesthetic styles preferred by a new combination of the functionals.

To compare the shapes preferred by the functionals, we built a robust surface optimization system. We represent shapes using Catmull--Clark subdivision surfaces, with the control mesh vertices acting as degrees of freedom for the optimization. The energy is minimized by an off-the-shelf implementation of a quasi-Newton method. We discuss some future work for further improving the optimization system and end with some conclusions on the use of optimization for aesthetic design.