Rule

The mathematical method for calculating the subdivisions.

• Catmull-Clark produces rounded shapes. The generated polygons are all quadrilateral. The higher the Subdivision Depth, the more this method approximates a bicubic standard B-spline surface. At regular vertices (exactly four edges), the surface has C2 (curvature) continuity; in other areas, the surface has C1 (tangential or parametric) continuity. The geometry produced is compatible with the method described in "Recursively generated B-spline surfaces on arbitrary topological surfaces" by E. Catmull and J. Clark (Computer-Aided Design 10(6):350-355, November 1978).

• XSI-Doo-Sabin produces shapes with the same silhouettes as traditional Doo-Sabin but with different tessellation. One advantage over traditional Doo-Sabin is that XSI-Doo-Sabin correctly propagates clusters and cluster properties (including discontinuities) such as texture UVs, vertex colors, and weight maps. Another advantage is that XSI-Doo-Sabin handles creases and hard edges better.

  Like traditional Doo-Sabin, XSI-Doo-Sabin produces shapes that follow the original mesh more closely than Catmull-Clark. If the original mesh has N polynodes, then each level L of subdivision has (4^L)N quad polygons. The higher the subdivision level, the more this method approximates a biquadratic uniform B-spline surface. At regular vertices, the surface has C1 (tangential or parametric) continuity; in other areas, the surface has G1 continuity (i.e., the tangents have the same direction but not necessarily the same length).

• Linear subdivides the mesh without smoothing it. This is useful when you want an object to deform well but do not want to change its basic shape.