Computing and Verifying Depth Orders

  • Authors:
  • Mark de Berg;Mark Overmars;Otfried Schwarzkopf

  • Affiliations:
  • -;-;-

  • Venue:
  • SIAM Journal on Computing
  • Year:
  • 1994

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Abstract

A depth order on a set of line segments in 3-space is an order such that line segment $a$ comes before line segment $a'$ in the order when $a$ lies below $a'$ or, in other words, when there is a vertical ray that first intersects $a'$ and then intersects $a$. Efficient algorithms for the computation and verification of depth orders of sets of $n$ line segments in 3-space are presented. The algorithms run in time $O(n^{4/3+\varepsilon})$, for any fixed $\varepsilon 0$. If all line segments are axis-parallel or, more generally, have only a constant number of different orientations, then the sorting algorithm runs in $O(n\log^3 n)$ time and the verification takes $O(n\log^2 n)$ time. The algorithms can be generalized to handle triangles and other polygons instead of line segments. They are based on a general framework for computing and verifying linear orders extending implicitly defined binary relations.