“…Most recent papers evolve from Blinn's original work [6] and vary mainly in the types of local implicit functions used, e.g., linear combination of Gaussian blobs [41], bounded polynomial in three variables [50], blended union of spheres [38], and, more recently, mixtures of globally supported radial basis functions (RBF's) [10,54], as well as blended compactly supported RBF's [47,43,33]. A line of recent improvements is the multi-level partition of unity implicits (MPU's) [42,44,53].…”