Stabbing Convex Bodies with Lines and Flats

Authors Sariel Har-Peled, Mitchell Jones

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Sariel Har-Peled
  • Department of Computer Science, University of Illinois at Urbana-Champaign, Urbana, Il, USA
Mitchell Jones
  • Department of Computer Science, University of Illinois at Urbana-Champaign, Urbana, IL, USA


We thank an anonymous reviewer for sketching an improved construction of (k, ε)-nets for k ≥ 1, which led to Theorem 6. Our previous construction had an additional log term.

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Sariel Har-Peled and Mitchell Jones. Stabbing Convex Bodies with Lines and Flats. In 37th International Symposium on Computational Geometry (SoCG 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 189, pp. 42:1-42:12, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)


We study the problem of constructing weak ε-nets where the stabbing elements are lines or k-flats instead of points. We study this problem in the simplest setting where it is still interesting - namely, the uniform measure of volume over the hypercube [0,1]^d. Specifically, a (k,ε)-net is a set of k-flats, such that any convex body in [0,1]^d of volume larger than ε is stabbed by one of these k-flats. We show that for k ≥ 1, one can construct (k,ε)-nets of size O(1/ε^{1-k/d}). We also prove that any such net must have size at least Ω(1/ε^{1-k/d}). As a concrete example, in three dimensions all ε-heavy bodies in [0,1]³ can be stabbed by Θ(1/ε^{2/3}) lines. Note, that these bounds are sublinear in 1/ε, and are thus somewhat surprising.

Subject Classification

ACM Subject Classification
  • Theory of computation → Computational geometry
  • Discrete geometry
  • combinatorics
  • weak ε-nets
  • k-flats


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