/*
* 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.revolsys.geometry.geomgraph.index;
import java.util.ArrayList;
import java.util.List;
import com.revolsys.geometry.geomgraph.Edge;
import com.revolsys.geometry.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.
* <p>
* Monotone Chains have the following useful 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.
*
* @version 1.7
*/
public class MonotoneChainIndexer {
public static int[] toIntArray(final List<Integer> list) {
final int[] array = new int[list.size()];
for (int i = 0; i < array.length; i++) {
array[i] = list.get(i);
}
return array;
}
public MonotoneChainIndexer() {
}
/**
* @return the index of the last point in the monotone chain
*/
private int findChainEnd(final Edge edge, final int start) {
// determine quadrant for chain
final int chainQuad = Quadrant.quadrant(edge.getPoint(start), edge.getPoint(start + 1));
int last = start + 1;
while (last < edge.getVertexCount()) {
// compute quadrant for next possible segment in chain
final int quad = Quadrant.quadrant(edge.getPoint(last - 1), edge.getPoint(last));
if (quad != chainQuad) {
break;
}
last++;
}
return last - 1;
}
public int[] getChainStartIndices(final Edge edge) {
// find the startpoint (and endpoints) of all monotone chains in this edge
int start = 0;
final List<Integer> startIndexList = new ArrayList<>();
startIndexList.add(start);
final int numPoints = edge.getVertexCount();
do {
final int last = findChainEnd(edge, start);
startIndexList.add(last);
start = last;
} while (start < numPoints - 1);
// copy list to an array of ints, for efficiency
final int[] startIndex = toIntArray(startIndexList);
return startIndex;
}
}