com.revolsys.jts.algorithm.distance

Class DiscreteHausdorffDistance

java.lang.Object

com.revolsys.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
 

Constructor Summary

Constructors

Constructor and Description
DiscreteHausdorffDistance(Geometry g0, Geometry g1)

Method Summary

Methods

Modifier and Type	Method and Description
double	distance()
static double	distance(Geometry g0, Geometry g1)
static double	distance(Geometry g0, Geometry g1, double densifyFrac)
Point[]	getCoordinates()
double	orientedDistance()
void	setDensifyFraction(double densifyFrac) Sets the fraction by which to densify each segment.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DiscreteHausdorffDistance

public DiscreteHausdorffDistance(Geometry g0,
                         Geometry g1)

Method Detail

distance

public static double distance(Geometry g0,
              Geometry g1)

distance

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

distance

public double distance()

getCoordinates

public Point[] getCoordinates()

orientedDistance

public double orientedDistance()

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:

densifyPercent -