CoordinateSequenceComparator.java

/*
* The JTS Topology Suite is a collection of Java classes that
* implement the fundamental operations required to validate a given
* geo-spatial data set to a known topological specification.
*
* Copyright (C) 2001 Vivid Solutions
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*
* For more information, contact:
*
*     Vivid Solutions
*     Suite #1A
*     2328 Government Street
*     Victoria BC  V8T 5G5
*     Canada
*
*     (250)385-6040
*     www.vividsolutions.com
*/

package com.vividsolutions.jts.geom;

import java.util.Comparator;

/**
 * Compares two {@link CoordinateSequence}s.
 * For sequences of the same dimension, the ordering is lexicographic.
 * Otherwise, lower dimensions are sorted before higher.
 * The dimensions compared can be limited; if this is done
 * ordinate dimensions above the limit will not be compared.
 * <p>
 * If different behaviour is required for comparing size, dimension, or
 * coordinate values, any or all methods can be overridden.
 *
 */
public class CoordinateSequenceComparator
	implements Comparator
{
  /**
   * Compare two <code>double</code>s, allowing for NaN values.
   * NaN is treated as being less than any valid number.
   *
   * @param a a <code>double</code>
   * @param b a <code>double</code>
   * @return -1, 0, or 1 depending on whether a is less than, equal to or greater than b
   */
  public static int compare(double a, double b)
  {
    if (a < b) return -1;
    if (a > b) return 1;

    if (Double.isNaN(a)) {
      if (Double.isNaN(b)) return 0;
      return -1;
    }

    if (Double.isNaN(b)) return 1;
    return 0;
  }

  /**
   * The number of dimensions to test
   */
  protected int dimensionLimit;

  /**
   * Creates a comparator which will test all dimensions.
   */
  public CoordinateSequenceComparator()
  {
    dimensionLimit = Integer.MAX_VALUE;
  }

  /**
   * Creates a comparator which will test only the specified number of dimensions.
   *
   * @param dimensionLimit the number of dimensions to test
   */
  public CoordinateSequenceComparator(int dimensionLimit)
  {
    this.dimensionLimit = dimensionLimit;
  }

  /**
   * Compares two {@link CoordinateSequence}s for relative order.
   *
   * @param o1 a {@link CoordinateSequence}
   * @param o2 a {@link CoordinateSequence}
   * @return -1, 0, or 1 depending on whether o1 is less than, equal to, or greater than o2
   */
  public int compare(Object o1, Object o2)
  {
    CoordinateSequence s1 = (CoordinateSequence) o1;
    CoordinateSequence s2 = (CoordinateSequence) o2;

    int size1 = s1.size();
    int size2 = s2.size();

    int dim1 = s1.getDimension();
    int dim2 = s2.getDimension();

    int minDim = dim1;
    if (dim2 < minDim)
      minDim = dim2;
    boolean dimLimited = false;
    if (dimensionLimit <= minDim) {
      minDim = dimensionLimit;
      dimLimited = true;
    }

    // lower dimension is less than higher
    if (! dimLimited) {
      if (dim1 < dim2) return -1;
      if (dim1 > dim2) return 1;
    }

    // lexicographic ordering of point sequences
    int i = 0;
    while (i < size1 && i < size2) {
      int ptComp = compareCoordinate(s1, s2, i, minDim);
      if (ptComp != 0) return ptComp;
      i++;
    }
    if (i < size1) return 1;
    if (i < size2) return -1;

    return 0;
  }

  /**
   * Compares the same coordinate of two {@link CoordinateSequence}s
   * along the given number of dimensions.
   *
   * @param s1 a {@link CoordinateSequence}
   * @param s2 a {@link CoordinateSequence}
   * @param i the index of the coordinate to test
   * @param dimension the number of dimensiosn to test
   * @return -1, 0, or 1 depending on whether s1[i] is less than, equal to, or greater than s2[i]
   */
  protected int compareCoordinate(CoordinateSequence s1, CoordinateSequence s2, int i, int dimension)
  {
    for (int d = 0; d < dimension; d++) {
      double ord1 = s1.getOrdinate(i, d);
      double ord2 = s2.getOrdinate(i, d);
      int comp = compare(ord1, ord2);
      if (comp != 0) return comp;
    }
    return 0;
  }
}