EVOLUTION-MANAGER

Edit File: MonotoneChainEdge.cpp

/**********************************************************************
 *
 * GEOS - Geometry Engine Open Source
 * http://geos.osgeo.org
 *
 * Copyright (C) 2005-2006 Refractions Research Inc.
 * Copyright (C) 2001-2002 Vivid Solutions Inc.
 *
 * This is free software; you can redistribute and/or modify it under
 * the terms of the GNU Lesser General Public Licence as published
 * by the Free Software Foundation.
 * See the COPYING file for more information.
 *
 **********************************************************************/

#include <cassert>
#include <vector>

#include <geos/geomgraph/Edge.h>
#include <geos/geomgraph/index/MonotoneChainEdge.h>
#include <geos/geomgraph/index/MonotoneChainIndexer.h>
#include <geos/geomgraph/index/SegmentIntersector.h>
#include <geos/geom/Coordinate.h>
#include <geos/geom/CoordinateSequence.h>

using namespace std;
using namespace geos::geom;

namespace geos {
namespace geomgraph { // geos.geomgraph
namespace index { // geos.geomgraph.index

/**
 * MonotoneChains are a way of partitioning the segments of an edge to
 * allow for fast searching of intersections.
 * They have the following 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.
 * @version 1.1
 */

MonotoneChainEdge::MonotoneChainEdge(Edge* newE):
    e(newE),
    pts(newE->getCoordinates())
{
    assert(e);
    MonotoneChainIndexer mci;
    mci.getChainStartIndices(pts, startIndex);
    assert(e);
}

const CoordinateSequence*
MonotoneChainEdge::getCoordinates()
{
    assert(pts);
    return pts;
}

vector<size_t>&
MonotoneChainEdge::getStartIndexes()
{
    return startIndex;
}

double
MonotoneChainEdge::getMinX(size_t chainIndex)
{
    double x1 = pts->getAt(startIndex[chainIndex]).x;
    double x2 = pts->getAt(startIndex[chainIndex + 1]).x;
    return x1 < x2 ? x1 : x2;
}

double
MonotoneChainEdge::getMaxX(size_t chainIndex)
{
    double x1 = pts->getAt(startIndex[chainIndex]).x;
    double x2 = pts->getAt(startIndex[chainIndex + 1]).x;
    return x1 > x2 ? x1 : x2;
}

void
MonotoneChainEdge::computeIntersects(const MonotoneChainEdge& mce,
                                     SegmentIntersector& si)
{
    size_t I = startIndex.size() - 1;
    size_t J = mce.startIndex.size() - 1;
    for(size_t i = 0; i < I; ++i) {
        for(size_t j = 0; j < J; ++j) {
            computeIntersectsForChain(i, mce, j, si);
        }
    }
}

void
MonotoneChainEdge::computeIntersectsForChain(size_t chainIndex0,
        const MonotoneChainEdge& mce, size_t chainIndex1,
        SegmentIntersector& si)
{
    computeIntersectsForChain(startIndex[chainIndex0],
                              startIndex[chainIndex0 + 1], mce,
                              mce.startIndex[chainIndex1],
                              mce.startIndex[chainIndex1 + 1],
                              si);
}

void
MonotoneChainEdge::computeIntersectsForChain(size_t start0, size_t end0,
        const MonotoneChainEdge& mce, size_t start1, size_t end1,
        SegmentIntersector& ei)
{
    // terminating condition for the recursion
    if(end0 - start0 == 1 && end1 - start1 == 1) {
        ei.addIntersections(e, start0, mce.e, start1);
        return;
    }

if(!overlaps(start0, end0, mce, start1, end1)) {
        return;
    }
    // the chains overlap, so split each in half and iterate
    // (binary search)
    size_t mid0 = (start0 + end0) / 2;
    size_t mid1 = (start1 + end1) / 2;

// Assert: mid != start or end
    // (since we checked above for end - start <= 1)
    // check terminating conditions before recursing
    if(start0 < mid0) {
        if(start1 < mid1)
            computeIntersectsForChain(start0, mid0, mce,
                                      start1, mid1, ei);
        if(mid1 < end1)
            computeIntersectsForChain(start0, mid0, mce,
                                      mid1, end1, ei);
    }
    if(mid0 < end0) {
        if(start1 < mid1)
            computeIntersectsForChain(mid0, end0, mce,
                                      start1, mid1, ei);
        if(mid1 < end1)
            computeIntersectsForChain(mid0, end0, mce,
                                      mid1, end1, ei);
    }
}

bool
MonotoneChainEdge::overlaps(size_t start0, size_t end0, const MonotoneChainEdge& mce, size_t start1, size_t end1)
{
    return Envelope::intersects(pts->getAt(start0), pts->getAt(end0),
                                mce.pts->getAt(start1), mce.pts->getAt(end1));
}

} // namespace geos.geomgraph.index
} // namespace geos.geomgraph
} // namespace geos