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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;
/**
* @version 1.7
*/
import java.util.*;
import com.vividsolutions.jts.geomgraph.*;
/**
* Finds all intersections in one or two sets of edges,
* using an x-axis sweepline algorithm in conjunction with Monotone Chains.
* While still O(n^2) in the worst case, this algorithm
* drastically improves the average-case time.
* The use of MonotoneChains as the items in the index
* seems to offer an improvement in performance over a sweep-line alone.
*
* @version 1.7
*/
public class SimpleMCSweepLineIntersector
extends EdgeSetIntersector
{
List events = new ArrayList();
// statistics information
int nOverlaps;
/**
* A SimpleMCSweepLineIntersector creates monotone chains from the edges
* and compares them using a simple sweep-line along the x-axis.
*/
public SimpleMCSweepLineIntersector() {
}
public void computeIntersections(List edges, SegmentIntersector si, boolean testAllSegments)
{
if (testAllSegments)
add(edges, null);
else
add(edges);
computeIntersections(si);
}
public void computeIntersections(List edges0, List edges1, SegmentIntersector si)
{
add(edges0, edges0);
add(edges1, edges1);
computeIntersections(si);
}
private void add(List edges)
{
for (Iterator i = edges.iterator(); i.hasNext(); ) {
Edge edge = (Edge) i.next();
// edge is its own group
add(edge, edge);
}
}
private void add(List edges, Object edgeSet)
{
for (Iterator i = edges.iterator(); i.hasNext(); ) {
Edge edge = (Edge) i.next();
add(edge, edgeSet);
}
}
private void add(Edge edge, Object edgeSet)
{
MonotoneChainEdge mce = edge.getMonotoneChainEdge();
int[] startIndex = mce.getStartIndexes();
for (int i = 0; i < startIndex.length - 1; i++) {
MonotoneChain mc = new MonotoneChain(mce, i);
SweepLineEvent insertEvent = new SweepLineEvent(edgeSet, mce.getMinX(i), mc);
events.add(insertEvent);
events.add(new SweepLineEvent(mce.getMaxX(i), insertEvent));
}
}
/**
* Because Delete Events have a link to their corresponding Insert event,
* it is possible to compute exactly the range of events which must be
* compared to a given Insert event object.
*/
private void prepareEvents()
{
Collections.sort(events);
// set DELETE event indexes
for (int i = 0; i < events.size(); i++ )
{
SweepLineEvent ev = (SweepLineEvent) events.get(i);
if (ev.isDelete()) {
ev.getInsertEvent().setDeleteEventIndex(i);
}
}
}
private void computeIntersections(SegmentIntersector si)
{
nOverlaps = 0;
prepareEvents();
for (int i = 0; i < events.size(); i++ )
{
SweepLineEvent ev = (SweepLineEvent) events.get(i);
if (ev.isInsert()) {
processOverlaps(i, ev.getDeleteEventIndex(), ev, si);
}
}
}
private void processOverlaps(int start, int end, SweepLineEvent ev0, SegmentIntersector si)
{
MonotoneChain mc0 = (MonotoneChain) ev0.getObject();
/**
* Since we might need to test for self-intersections,
* include current INSERT event object in list of event objects to test.
* Last index can be skipped, because it must be a Delete event.
*/
for (int i = start; i < end; i++ ) {
SweepLineEvent ev1 = (SweepLineEvent) events.get(i);
if (ev1.isInsert()) {
MonotoneChain mc1 = (MonotoneChain) ev1.getObject();
// don't compare edges in same group, if labels are present
if (! ev0.isSameLabel(ev1)) {
mc0.computeIntersections(mc1, si);
nOverlaps++;
}
}
}
}
}