On the support of recursive subdivision

  • Authors:
  • Ioannis P. Ivrissimtzis;Malcolm A. Sabin;Neil A. Dodgson

  • Affiliations:
  • Max-planck-institut für Informatik, Saarbrücken, Germany;Numerical Geometry Ltd., Cambridge, England;University of Cambridge Computer Laboratory, Cambridge, England

  • Venue:
  • ACM Transactions on Graphics (TOG)
  • Year:
  • 2004

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Abstract

We study the support of subdivision schemes: that is, the region of the subdivision surface that is affected by the displacement of a single control point. Our main results cover the regular case, where the mesh induces a regular Euclidean tesselation of the local parameter space. If n is the ratio of similarity between the tesselations at steps k and k − 1 of the refinement, we show that n determines the extent of this region and largely determines whether its boundary is polygonal or fractal. In particular if n = 2 (or n2 = 2 because we can always take double steps) the support is a convex polygon whose vertices can easily be determined. In other cases, whether the boundary of the support is fractal or not depends on whether there are sufficient points with non-zero coefficients in the edges of the convex hull of the mask. If there are enough points on every such edge, the support is again a convex polygon. If some edges have enough points and others do not, the boundary can consist of a fractal assembly of an unbounded number of line segments.