Order on Order Types

Alexander Pilz, Emo Welzl

Research output: Chapter in Book/Report/Conference proceedingConference paperpeer-review


Given P and P′, equally sized planar point sets in general position, we call a bijection from P to P′ crossing-preserving if crossings of connecting segments in P are preserved in P′ (extra crossings may occur in P′). If such a mapping exists, we say that P′ crossing-dominates P, and if such a mapping exists in both directions, P and P′ are called crossing-equivalent. The relation is transitive, and we have a partial order on the obtained equivalence classes (called crossing types or x-types). Point sets of equal order type are clearly crossing-equivalent, but not vice versa. Thus, x-types are a coarser classification than order types. (We will see, though, that a collapse of different order types to one x-type occurs for sets with triangular convex hull only.) We argue that either the maximal or the minimal x-types are sufficient for answering many combinatorial (existential or extremal) questions on planar point sets. Motivated by this we consider basic properties of the relation. We characterize order types crossing-dominated by points in convex position. Further, we give a full characterization of minimal and maximal abstract order types. Based on that, we provide a polynomial-time algorithm to check whether a point set crossing-dominates another. Moreover, we generate all maximal and minimal x-types for small numbers of points.

Original languageEnglish
Title of host publication31st International Symposium on Computational Geometry, SoCG 2015
PublisherSchloss Dagstuhl - Leibniz-Zentrum für Informatik
Number of pages15
ISBN (Electronic)9783939897835
Publication statusPublished - 1 Jun 2015
Event31st International Symposium on Computational Geometry, SoCG 2015: SoCG 2015 - Eindhoven, Netherlands
Duration: 22 Jun 201525 Jun 2015


Conference31st International Symposium on Computational Geometry, SoCG 2015
Abbreviated titleSoCG 2015


  • Crossing-free geometric graph
  • Order type
  • Planar graph
  • Point set

ASJC Scopus subject areas

  • Software


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