/*
* GeoTools - The Open Source Java GIS Toolkit
* http://geotools.org
*
* (C) 2001-2006 Vivid Solutions
* (C) 2001-2008, Open Source Geospatial Foundation (OSGeo)
*
* 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;
* version 2.1 of the License.
*
* 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.
*/
package org.geotools.geometry.iso.topograph2D.index;
import java.util.ArrayList;
import java.util.List;
import org.geotools.geometry.iso.topograph2D.Coordinate;
import org.geotools.geometry.iso.topograph2D.Quadrant;
/**
* MonotoneChains are a way of partitioning the segments of an edge to allow for
* fast searching of intersections. They have the following properties:
* <ol>
* <li>the segments within a monotone chain will never intersect each other
* <li>the envelope of any contiguous subset of the segments in a monotone
* chain is simply the envelope of the endpoints of the subset.
* </ol>
* 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.
*
*
* @source $URL$
*/
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) {
// 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;
}
}