On lines missing polyhedral sets in 3-space

  • Authors:
  • Marco Pellegrini

  • Affiliations:
  • -

  • Venue:
  • SCG '93 Proceedings of the ninth annual symposium on Computational geometry
  • Year:
  • 1993

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Abstract

We study some combinatorial and algorithmic problems onsets of lines and polyhedral objects in 3-space. Our main resultsinclude:(1) An On32clogn upper bound on the worst case complexity of the setof lines missing a star-shaped compact polyhedron withn edges.(2) Given a star-shaped compact polyhedron P withn edges we can compute on-line theshadow of P from a query directionv in almost-optimal output-sensitivetime O(k log4n), where k is thesize of the shadow. The storage used by the data structure isO(n3+&egr;.(3) An On32clogn upper bound on the worst case complexity of the setof lines that can be moved to infinity without intersecting a set ofn given lines. This bound is almosttight.(4) AnO(n1.5+&egr;)randomized expected time algorithm that tests the separation property:there exists a direction v alongwhich a set of n red lines can betranslated away from a set of n bluelines without collisions?(5) Computing the intersection of two polyhedral terrains in3-space with n edges in timeO(n4/3+&egr; +k1/3n1+&egr; + klog2 n), where k is the size of the output, and&egr; 0 an arbitrary small but fixed constant. This algorithmimproves on the best previous result of Chazelle et al. [7]The tools used to obtain these results include Plu¨ckercoordinates of lines, random sampling and polarity transformations in3-space.