PolygonNodeTopology.h

/**********************************************************************
 *
 * GEOS - Geometry Engine Open Source
 * http://libgeos.org
 *
 * Copyright (c) 2021 Martin Davis
 * Copyright (C) 2022 Paul Ramsey <pramsey@cleverlephant.ca>
 *
 * 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.
 *
 **********************************************************************/

#pragma once

#include <geos/export.h>


// Forward declarations
namespace geos {
namespace geom {
class CoordinateXY;
}
}

using geos::geom::CoordinateXY;


namespace geos {
namespace algorithm { // geos::algorithm

class GEOS_DLL PolygonNodeTopology {

public:

    /*
    * Check if the segments at a node between two rings (or one ring) cross.
    * The node is topologically valid if the rings do not cross.
    * This function assumes that the segments are not collinear.
    *
    * @param nodePt the node location
    * @param a0 the previous segment endpoint in a ring
    * @param a1 the next segment endpoint in a ring
    * @param b0 the previous segment endpoint in the other ring
    * @param b1 the next segment endpoint in the other ring
    * @return true if the rings cross at the node
    */
    static bool
    isCrossing(const CoordinateXY* nodePt,
        const CoordinateXY* a0, const CoordinateXY* a1,
        const CoordinateXY* b0, const CoordinateXY* b1);


    static bool isInteriorSegment(const CoordinateXY* nodePt,
        const CoordinateXY* a0, const CoordinateXY* a1, const CoordinateXY* b);

    static int compareAngle(
        const CoordinateXY* origin,
        const CoordinateXY* p,
        const CoordinateXY* q);


private:

    static bool isBetween(const CoordinateXY* origin,
        const CoordinateXY* p,
        const CoordinateXY* e0, const CoordinateXY* e1);

    static int compareBetween(const CoordinateXY* origin, const CoordinateXY* p,
        const CoordinateXY* e0, const CoordinateXY* e1);


    static bool isAngleGreater(const CoordinateXY* origin, const CoordinateXY* p, const CoordinateXY* q);

    static int quadrant(const CoordinateXY* origin, const CoordinateXY* p);


};


} // namespace geos::algorithm
} // namespace geos