Randomized incremental constructions of three-dimensional convex hulls and planar voronoi diagrams, and approximate range counting

  • Authors:
  • Haim Kaplan;Micha Sharir

  • Affiliations:
  • Tel Aviv University, Tel Aviv, Israel;Tel Aviv University, Tel Aviv, Israel

  • Venue:
  • SODA '06 Proceedings of the seventeenth annual ACM-SIAM symposium on Discrete algorithm
  • Year:
  • 2006

Quantified Score

Hi-index 0.00

Visualization

Abstract

We present new algorithms for approximate range counting, where, for a specified ε 0, we want to count the number of data points in a query range, up to relative error of ε. We first describe a general framework, adapted from Cohen [10], for this task, and then specialize it to two important instances of range counting: halfspaces in R3 and disks in the plane. The technique reduces the approximate range counting problem to that of finding the minimum rank of a data object in the range, with respect to a random permutation of the input.A major technical step in our analysis, which we believe to be of independent interest, is a bound of O(n log n) on the expected complexity of the overlay of all the Voronoi faces that are generated during a randomized incremental construction of the Voronoi diagram of n points in the plane. The same bound holds for the expected complexity of the overlay of all the faces of the minimization diagram of the lower envelope of n planes in R3, or for the expected complexity of the overlay of all the normal (or Gaussian) diagram faces of the convex hull of n points in R3, that are generated during a randomized incremental construction of the lower envelope or of the hull, respectively. All these bounds are tight in the worst case.The first bound leads to an algorithm that, for a query point x ∈ R2, efficiently retrieves the sequence of nearest neighbors of x in P, over the random insertion process. A query takes O(log n) expected time, and the expected storage size is O(n log n). Similarly, the other bounds lead to an algorithm that, for a query direction ω ∈ S2, efficiently retrieves the sequence of the convex hull vertices that are touched by the planes with outward direction ω that support the convex hull during the random insertion process. Again, a query takes O(log n) expected time, and the expected storage size is O(n log n). These algorithms are used as the main component in the approximate range counting technique that we present, for ranges that are halfspaces in R3 or disks in the plane.