Relative Convex Hulls in Semi-dynamic Subdivisions

  • Authors:
  • Mashhood Ishaque;Csaba D. Tóth

  • Affiliations:
  • Dept. of Comp. Sci., Tufts University, Medford;Dept. of Mathematics, University of Calgary

  • Venue:
  • ESA '08 Proceedings of the 16th annual European symposium on Algorithms
  • Year:
  • 2008

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Abstract

We present data structures for maintaining the relative convex hull of a set of points (sites) in the presence of pairwise non-crossing line segments (barriers) that subdivide a bounding box into simply connected faces. Our data structures have O((n+ m)logn) size for nsites and mbarriers. They support O(m) barrier insertions and O(n) site deletions in O((m+ n) polylog (mn)) total time, and can answer analogues of standard convex hull queries in O(polylog(mn)) time.Our data structures support a generalization of the sweep line technique, in which the sweep wavefrontmay have arbitrary polygonal shape, possibly bending around obstacles. We reduce the total time of monline updates of a polygonal sweep wavefront from $O(m\sqrt{n}\,{\rm polylog} n)$ to O((m+ n) polylog (mn)).