k-sets of convex inclusion chains of planar point sets

  • Authors:
  • Wael El Oraiby;Dominique Schmitt

  • Affiliations:
  • Laboratoire MIA, Université de Haute-Alsace, Mulhouse Cedex, France;Laboratoire MIA, Université de Haute-Alsace, Mulhouse Cedex, France

  • Venue:
  • MFCS'06 Proceedings of the 31st international conference on Mathematical Foundations of Computer Science
  • Year:
  • 2006

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Abstract

Given a set V of n points in the plane, we introduce a new number of k-sets that is an invariant of V: the number of k-sets of a convex inclusion chain of V. A convex inclusion chain of V is an ordering (v1, v2, ..., vn) of the points of V such that no point of the ordering belongs to the convex hull of its predecessors. The k-sets of such a chain are then the distinct k-sets of all the subsets {v1, ..., vi}, for all i in {k+1, ..., n}. We show that the number of these k-sets depends only on V and not on the chosen convex inclusion chain. Moreover, this number is surprisingly equal to the number of regions of the order-k Voronoi diagram of V. As an application, we give an efficient on-line algorithm to compute the k-sets of the vertices of a simple polygonal line, no vertex of which belonging to the convex hull of its predecessors on the line.