L-system specification of knot-insertion rules for non-uniform B-spline subdivision

  • Authors:
  • V. Nivoliers;C. Gérot;V. Ostromoukhov;N. F. Stewart

  • Affiliations:
  • ALICE, Inria, France;GIPSA-lab, Grenoble, France;LIRIS, CNRS, France;LIGUM, Université de Montréal, Canada

  • Venue:
  • Computer Aided Geometric Design
  • Year:
  • 2012

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Abstract

Subdivision schemes are based on a hierarchy of knot grids in parameter space. A univariate grid hierarchy is regular if all knots are equidistant on each level, and irregular otherwise. We use L-systems to design a wide class of systematically described irregular grid hierarchies. Furthermore, we give sufficient conditions on the L-system which guarantee that the subdivision scheme, based on the non-uniform B-spline of degree d defined on the initial knot grid, is uniformly convergent. If n is the number of symbols in the alphabet of the L-system, this subdivision scheme is defined with a finite set of masks (at most n^d^+^1) which does not depend on the subdivision step. We provide an implementation of such schemes which is available as a worksheet for Sage software.