1. Introduction
Parametric surface modeling is an important research topic in 3D data processing, where a pre-defined mathematic model is used to describe a surface. Typical techniques include spherical harmonics (SHs) [2], [4], hyperquadrics [14], and superquadrics [23]. Recently, the SH method has received a lot attention, and has been studied and applied to several areas including computer vision [2], [4], computer graphics [5], [10], [24], medical image analysis [11], [12], [16], [20], [21], and computational biology [19].