com.vividsolutions.jts.geomgraph.index.MonotoneChainIndexer Maven / Gradle / Ivy
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/*
* 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.Coordinate;
import com.vividsolutions.jts.geomgraph.Quadrant;
/**
* MonotoneChains are a way of partitioning the segments of an edge to
* allow for fast searching of intersections.
* Specifically, a sequence of contiguous line segments
* is a monotone chain iff all the vectors defined by the oriented segments
* lies in the same quadrant.
*
* Monotone Chains have the following useful properties:
*
* - the segments within a monotone chain will never intersect each other
*
- the envelope of any contiguous subset of the segments in a monotone chain
* is simply the envelope of the endpoints of the subset.
*
* Property 1 means that there is no need to test pairs of segments from within
* the same monotone chain for intersection.
* Property 2 allows
* binary search to be used to find the intersection points of two monotone chains.
* For many types of real-world data, these properties eliminate a large number of
* segment comparisons, producing substantial speed gains.
*
* Note that due to the efficient intersection test, there is no need to limit the size
* of chains to obtain fast performance.
*
* @version 1.7
*/
public class MonotoneChainIndexer {
public static int[] toIntArray(List list)
{
int[] array = new int[list.size()];
for (int i = 0; i < array.length; i++) {
array[i] = ((Integer) list.get(i)).intValue();
}
return array;
}
public MonotoneChainIndexer() {
}
public int[] getChainStartIndices(Coordinate[] pts)
{
// find the startpoint (and endpoints) of all monotone chains in this edge
int start = 0;
List startIndexList = new ArrayList();
startIndexList.add(new Integer(start));
do {
int last = findChainEnd(pts, start);
startIndexList.add(new Integer(last));
start = last;
} while (start < pts.length - 1);
// copy list to an array of ints, for efficiency
int[] startIndex = toIntArray(startIndexList);
return startIndex;
}
/**
* @return the index of the last point in the monotone chain
*/
private int findChainEnd(Coordinate[] pts, int start)
{
// determine quadrant for chain
int chainQuad = Quadrant.quadrant(pts[start], pts[start + 1]);
int last = start + 1;
while (last < pts.length ) {
//if (last - start > 100) break;
// compute quadrant for next possible segment in chain
int quad = Quadrant.quadrant(pts[last - 1], pts[last]);
if (quad != chainQuad) break;
last++;
}
return last - 1;
}
}