Intersecting convex sets by rays

  • Authors:
  • Radoslav Fulek;Andreas F. Holmsen;János Pach

  • Affiliations:
  • Simon Fraser University, Burnaby, Canada;Korea Advanced Institute of Science and Technology, Daejon, South Korea;City College of New York, New York, NY, USA

  • Venue:
  • Proceedings of the twenty-fourth annual symposium on Computational geometry
  • Year:
  • 2008

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Abstract

What is the smallest number τ = τ(n) such that for any collection of n pairwise disjoint convex sets in d-dimensional Euclidean space, there is a point such that any ray (half-line) emanating from it meets at most τ sets of the collection? This question of Urrutia is closely related to the notion of regression depth introduced by Rousseeuw and Hubert (1996). We show the following: Given any collection C of n pairwise disjoint compact convex sets in d-dimensional Euclidean space, there exists a point p such that any ray emanating from p meets at most dn+1)/d+1) members of C. There exist collections of n pairwise disjoint (i) equal length segments or (ii) disks in the Euclidean plane such that from any point there is a ray that meets at least 2n/3--2 of them. We also determine the asymptotic behavior of τ(n) when the convex bodies are fat and of roughly equal size.