On Regular Vertices of the Union of Planar Convex Objects

  • Authors:
  • Esther Ezra;János Pach;Micha Sharir

  • Affiliations:
  • Tel Aviv University, School of Computer Science, 69978, Tel Aviv, Israel;City College, CUNY, Department of Computer Science, Convent Ave. at 138th St., 10031, New York, NY, USA and New York Univ., Courant Inst. of Mathematical Sciences, 10012, New York, NY, USA and Ren ...;New York University, Courant Institute of Mathematical Sciences, 10012, New York, NY, USA and Renyi Institute, P.O. Box 127, 1364, Budapest, Hungary

  • Venue:
  • Discrete & Computational Geometry
  • Year:
  • 2009

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Abstract

Let $\mathcal{C}$be a collection of n compact convex sets in the plane such that the boundaries of any pair of sets in $\mathcal{C}$intersect in at most s points for some constant s≥4. We show that the maximum number of regular vertices (intersection points of two boundaries that intersect twice) on the boundary of the union U of $\mathcal{C}$is O *(n 4/3), which improves earlier bounds due to Aronov et al. (Discrete Comput. Geom. 25, 203–220, 2001). The bound is nearly tight in the worst case. In this paper, a bound of the form O *(f(n)) means that the actual bound is C ε f(n)⋅n ε for any ε0, where C ε is a constant that depends on ε (and generally tends to ∞ as ε decreases to 0).