SegmentPointComparator.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.noding;

import com.vividsolutions.jts.geom.Coordinate;
import com.vividsolutions.jts.util.Assert;

/**
 * Implements a robust method of comparing the relative position of two
 * points along the same segment.
 * The coordinates are assumed to lie "near" the segment.
 * This means that this algorithm will only return correct results
 * if the input coordinates
 * have the same precision and correspond to rounded values
 * of exact coordinates lying on the segment.
 *
 * @version 1.7
 */
public class SegmentPointComparator {

  /**
   * Compares two {@link Coordinate}s for their relative position along a segment
   * lying in the specified {@link Octant}.
   *
   * @return -1 node0 occurs first;
   * 0 the two nodes are equal;
   * 1 node1 occurs first
   */
  public static int compare(int octant, Coordinate p0, Coordinate p1)
  {
    // nodes can only be equal if their coordinates are equal
    if (p0.equals2D(p1)) return 0;

    int xSign = relativeSign(p0.x, p1.x);
    int ySign = relativeSign(p0.y, p1.y);

    switch (octant) {
      case 0: return compareValue(xSign, ySign);
      case 1: return compareValue(ySign, xSign);
      case 2: return compareValue(ySign, -xSign);
      case 3: return compareValue(-xSign, ySign);
      case 4: return compareValue(-xSign, -ySign);
      case 5: return compareValue(-ySign, -xSign);
      case 6: return compareValue(-ySign, xSign);
      case 7: return compareValue(xSign, -ySign);
    }
    Assert.shouldNeverReachHere("invalid octant value");
    return 0;
  }

  public static int relativeSign(double x0, double x1)
  {
    if (x0 < x1) return -1;
    if (x0 > x1) return 1;
    return 0;
  }

  private static int compareValue(int compareSign0, int compareSign1)
  {
    if (compareSign0 < 0) return -1;
    if (compareSign0 > 0) return 1;
    if (compareSign1 < 0) return -1;
    if (compareSign1 > 0) return 1;
    return 0;

  }
}