Doo-Sabin Surfaces Generalization of uniform biquadratic B-spline surfaces to meshes of arbitrary topology [Doo and Sabin 1978]. Limit point rule:For an n-sided face, its centroid is the limit position of its associated extraordinary point. The extraordinary points are at the "centers"of n-sided faces. Convergence:The Doo-Sabin refinement is convergent for extraordinary points with arbitrary valence. Z Huang.G Wang Non-Uniform Recursive Doo-Sabin Surtaces (NURDSes) Doo-Sabin Surfaces Generalization of uniform biquadratic B-spline surfaces to meshes of arbitrary topology [Doo and Sabin 1978]. Limit point rule: For an n-sided face, its centroid is the limit position of its associated extraordinary point. The extraordinary points are at the "centers" of n-sided faces. Convergence: The Doo-Sabin refinement is convergent for extraordinary points with arbitrary valence. Z Huang, G Wang Non-Uniform Recursive Doo-Sabin Surfaces (NURDSes)