SegmentIntersector.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.geomgraph.index;

import java.util.*;
import com.vividsolutions.jts.geom.*;
import com.vividsolutions.jts.geomgraph.*;
import com.vividsolutions.jts.algorithm.LineIntersector;
import com.vividsolutions.jts.util.Debug;


/**
 * Computes the intersection of line segments,
 * and adds the intersection to the edges containing the segments.
 * 
 * @version 1.7
 */
public class SegmentIntersector 
{

  public static boolean isAdjacentSegments(int i1, int i2)
  {
    return Math.abs(i1 - i2) == 1;
  }

  /**
   * These variables keep track of what types of intersections were
   * found during ALL edges that have been intersected.
   */
  private boolean hasIntersection = false;
  private boolean hasProper = false;
  private boolean hasProperInterior = false;
  // the proper intersection point found
  private Coordinate properIntersectionPoint = null;

  private LineIntersector li;
  private boolean includeProper;
  private boolean recordIsolated;
  private boolean isSelfIntersection;
  //private boolean intersectionFound;
  private int numIntersections = 0;

  // testing only
  public int numTests = 0;

  private Collection[] bdyNodes;
/*
  public SegmentIntersector()
  {
  }
*/
  public SegmentIntersector(LineIntersector li,  boolean includeProper, boolean recordIsolated)
  {
    this.li = li;
    this.includeProper = includeProper;
    this.recordIsolated = recordIsolated;
  }

  public void setBoundaryNodes( Collection bdyNodes0,
                              Collection bdyNodes1)
  {
      bdyNodes = new Collection[2];
      bdyNodes[0] = bdyNodes0;
      bdyNodes[1] = bdyNodes1;
  }

  /**
   * @return the proper intersection point, or <code>null</code> if none was found
   */
  public Coordinate getProperIntersectionPoint()  {    return properIntersectionPoint;  }

  public boolean hasIntersection() { return hasIntersection; }
  /**
   * A proper intersection is an intersection which is interior to at least two
   * line segments.  Note that a proper intersection is not necessarily
   * in the interior of the entire Geometry, since another edge may have
   * an endpoint equal to the intersection, which according to SFS semantics
   * can result in the point being on the Boundary of the Geometry.
   */
  public boolean hasProperIntersection() { return hasProper; }
  /**
   * A proper interior intersection is a proper intersection which is <b>not</b>
   * contained in the set of boundary nodes set for this SegmentIntersector.
   */
  public boolean hasProperInteriorIntersection() { return hasProperInterior; }


  /**
   * A trivial intersection is an apparent self-intersection which in fact
   * is simply the point shared by adjacent line segments.
   * Note that closed edges require a special check for the point shared by the beginning
   * and end segments.
   */
  private boolean isTrivialIntersection(Edge e0, int segIndex0, Edge e1, int segIndex1)
  {
    if (e0 == e1) {
      if (li.getIntersectionNum() == 1) {
        if (isAdjacentSegments(segIndex0, segIndex1))
          return true;
        if (e0.isClosed()) {
          int maxSegIndex = e0.getNumPoints() - 1;
          if (    (segIndex0 == 0 && segIndex1 == maxSegIndex)
              ||  (segIndex1 == 0 && segIndex0 == maxSegIndex) ) {
            return true;
          }
        }
      }
    }
    return false;
  }

  /**
   * This method is called by clients of the EdgeIntersector class to test for and add
   * intersections for two segments of the edges being intersected.
   * Note that clients (such as MonotoneChainEdges) may choose not to intersect
   * certain pairs of segments for efficiency reasons.
   */
  public void addIntersections(
    Edge e0,  int segIndex0,
    Edge e1,  int segIndex1
     )
  {
    if (e0 == e1 && segIndex0 == segIndex1) return;
numTests++;
    Coordinate p00 = e0.getCoordinates()[segIndex0];
    Coordinate p01 = e0.getCoordinates()[segIndex0 + 1];
    Coordinate p10 = e1.getCoordinates()[segIndex1];
    Coordinate p11 = e1.getCoordinates()[segIndex1 + 1];

    li.computeIntersection(p00, p01, p10, p11);
//if (li.hasIntersection() && li.isProper()) Debug.println(li);
    /**
     *  Always record any non-proper intersections.
     *  If includeProper is true, record any proper intersections as well.
     */
    if (li.hasIntersection()) {
      if (recordIsolated) {
        e0.setIsolated(false);
        e1.setIsolated(false);
      }
      //intersectionFound = true;
      numIntersections++;
      // if the segments are adjacent they have at least one trivial intersection,
      // the shared endpoint.  Don't bother adding it if it is the
      // only intersection.
      if (! isTrivialIntersection(e0, segIndex0, e1, segIndex1)) {
        hasIntersection = true;
        if (includeProper || ! li.isProper() ) {
//Debug.println(li);
          e0.addIntersections(li, segIndex0, 0);
          e1.addIntersections(li, segIndex1, 1);
        }
        if (li.isProper()) {
          properIntersectionPoint = (Coordinate) li.getIntersection(0).clone();
          hasProper = true;
          if (! isBoundaryPoint(li, bdyNodes))
            hasProperInterior = true;
        }
        //if (li.isCollinear())
          //hasCollinear = true;
      }
    }
  }

  private boolean isBoundaryPoint(LineIntersector li, Collection[] bdyNodes)
  {
    if (bdyNodes == null) return false;
    if (isBoundaryPoint(li, bdyNodes[0])) return true;
    if (isBoundaryPoint(li, bdyNodes[1])) return true;
    return false;
  }

  private boolean isBoundaryPoint(LineIntersector li, Collection bdyNodes)
  {
    for (Iterator i = bdyNodes.iterator(); i.hasNext(); ) {
      Node node = (Node) i.next();
      Coordinate pt = node.getCoordinate();
      if (li.isIntersection(pt)) return true;
    }
    return false;
  }

}