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Adaptive algorithms for constructing convex hulls and triangulations of polygonal chains

Author

Summary, in English

We study some fundamental computational geometry problems with the goal to exploit structure in input data that is given as a sequence C = (p(1), p(2), . . . ,p(n)) of points that are "almost sorted" in the sense that the polygonal chain they define has a possibly small number, k, of self-intersections, or the chain can be partitioned into a small number, X, of simple subchains. We give results that show adaptive complexity in terms of k or X: when k or X is small compared to n, we achieve time bounds that approach the linear-time (O(n)) bounds known for the corresponding problems on simple polygonal chains. In particular, we show that the convex hull of C can be computed in O(n log(X + 2)) time, and prove a matching lower bound of Omega(n log(X + 2)) in the algebraic decision tree model. We also prove a lower bound of Omega(n log(k/n)) for k > n in the algebraic decision tree model; since X less than or equal to k, the upper bound of O(n log(k + 2)) follows. We also show that a polygonal chain with k proper inter sections can be transformed into a polygonal chain without proper intersections by adding at most 2k new vertices in time O(n (.) min{rootk, log n} + k). This yields O(n (.) min{rootk, log n} + k)-time algorithms for triangulation, in particular the constrained Delaunay triangulation of a polygonal chain where the proper intersection points are also regarded as vertices.

Department/s

  • Computer Science

Publishing year

2002

Language

English

Pages

80-89

Publication/Series

Algorithm Theory - SWAT 2002 / Lecture Notes in Computer Science

Volume

2368

Document type

Conference paper

Publisher

Springer

Topic

  • Computer Science

Keywords

  • upper bound
  • lower bound
  • algebraic decision tree model
  • polygonal chains
  • constrained Delaunay triangulation
  • adaptive complexity
  • triangulations of polygonal chains
  • polygonal chain
  • computational geometry
  • adaptive algorithms
  • convex hulls

Conference name

8th Scandinavian Workshop on Algorithm Theory.

Conference date

2002-07-03 - 2002-07-05

Conference place

Turku, Finland

Status

Published

ISBN/ISSN/Other

  • ISSN: 0302-9743
  • ISSN: 1611-3349