Class DiscreteHausdorffDistance

java.lang.Object
org.locationtech.jts.algorithm.distance.DiscreteHausdorffDistance

public class DiscreteHausdorffDistance extends Object
An algorithm for computing a distance metric which is an approximation to the Hausdorff Distance based on a discretization of the input Geometry. The algorithm computes the Hausdorff distance restricted to discrete points for one of the geometries. The points can be either the vertices of the geometries (the default), or the geometries with line segments densified by a given fraction. Also determines two points of the Geometries which are separated by the computed distance.

This algorithm is an approximation to the standard Hausdorff distance. Specifically,

    for all geometries a, b:    DHD(a, b) <= HD(a, b)
 
The approximation can be made as close as needed by densifying the input geometries. In the limit, this value will approach the true Hausdorff distance:
    DHD(A, B, densifyFactor) -> HD(A, B) as densifyFactor -> 0.0
 
The default approximation is exact or close enough for a large subset of useful cases. Examples of these are:
  • computing distance between Linestrings that are roughly parallel to each other, and roughly equal in length. This occurs in matching linear networks.
  • Testing similarity of geometries.
An example where the default approximation is not close is:
   A = LINESTRING (0 0, 100 0, 10 100, 10 100)
   B = LINESTRING (0 100, 0 10, 80 10)
   
   DHD(A, B) = 22.360679774997898
   HD(A, B) ~= 47.8
 
  • Field Details

    • g0

      private Geometry g0
    • g1

      private Geometry g1
    • ptDist

      private PointPairDistance ptDist
    • densifyFrac

      private double densifyFrac
      Value of 0.0 indicates that no densification should take place
  • Constructor Details

    • DiscreteHausdorffDistance

      public DiscreteHausdorffDistance(Geometry g0, Geometry g1)
  • Method Details

    • distance

      public static double distance(Geometry g0, Geometry g1)
    • distance

      public static double distance(Geometry g0, Geometry g1, double densifyFrac)
    • setDensifyFraction

      public void setDensifyFraction(double densifyFrac)
      Sets the fraction by which to densify each segment. Each segment will be (virtually) split into a number of equal-length subsegments, whose fraction of the total length is closest to the given fraction.
      Parameters:
      densifyFrac -
    • distance

      public double distance()
    • orientedDistance

      public double orientedDistance()
    • getCoordinates

      public Coordinate[] getCoordinates()
    • compute

      private void compute(Geometry g0, Geometry g1)
    • computeOrientedDistance

      private void computeOrientedDistance(Geometry discreteGeom, Geometry geom, PointPairDistance ptDist)