Convex hulls of spheres and convex hulls of disjoint convex polytopes

  • Authors:
  • Menelaos I. Karavelas;Raimund Seidel;Eleni Tzanaki

  • Affiliations:
  • University of Crete, Department of Applied Mathematics, GR-714 09 Heraklion, Greece and Foundation for Research and Technology - Hellas, Institute of Applied and Computational Mathematics, PO Box ...;Fachrichtung Informatik, Universität des Saarlandes, Postfach 151150, D-66041 Saarbrücken, Germany;University of Crete, Department of Applied Mathematics, GR-714 09 Heraklion, Greece and Foundation for Research and Technology - Hellas, Institute of Applied and Computational Mathematics, PO Box ...

  • Venue:
  • Computational Geometry: Theory and Applications
  • Year:
  • 2013

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Abstract

Given a set @S of spheres in E^d, with d=3 and d odd, having a constant number of m distinct radii @r"1,@r"2,...,@r"m, we show that the worst-case combinatorial complexity of the convex hull of @S is @Q(@?"1"="j"==3 odd, where n"i spheres have radius @r"i, i=1,2, and @r"2@r"1, such that their convex hull has combinatorial complexity @W(n"1n"2^@?^d^2^@?+n"2n"1^@?^d^2^@?). Our construction is then generalized to the case where the spheres have m=3 distinct radii. For the upper bound, we reduce the sphere convex hull problem to the problem of computing the worst-case combinatorial complexity of the convex hull of a set of m disjoint d-dimensional convex polytopes in E^d^+^1, where d=3 odd, a problem which is of independent interest. More precisely, we show that the worst-case combinatorial complexity of the convex hull of a set of m disjoint d-dimensional convex polytopes in E^d^+^1 is O(@?"1"="j"==3. Finally, we discuss how to compute convex hulls of spheres with a constant number of distinct radii, or convex hulls of a constant number of disjoint convex polytopes.