EVOLUTION-MANAGER

Edit File: Orientation.h

/**********************************************************************
 *
 * GEOS - Geometry Engine Open Source
 * http://geos.osgeo.org
 *
 * Copyright (C) 2018 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.
 *
 **********************************************************************
 *
 * Last port: algorithm/Orientation.java @ 2017-09-04
 *
 **********************************************************************/

#ifndef GEOS_ALGORITHM_ORIENTATION_H
#define GEOS_ALGORITHM_ORIENTATION_H

#include <geos/export.h>
#include <geos/geom/Coordinate.h>
#include <geos/geom/CoordinateSequence.h>

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

/** \brief
 * Functions to compute the orientation of basic geometric structures
 * including point triplets (triangles) and rings.
 *
 * Orientation is a fundamental property of planar geometries
 * (and more generally geometry on two-dimensional manifolds).
 *
 * Orientation is notoriously subject to numerical precision errors
 * in the case of collinear or nearly collinear points.
 * JTS uses extended-precision arithmetic to increase
 * the robustness of the computation.
 *
 * @author Martin Davis
 */
class GEOS_DLL Orientation {
public:

/* A value that indicates an orientation or turn */
    enum {
        CLOCKWISE = -1,
        COLLINEAR = 0,
        COUNTERCLOCKWISE = 1,
        RIGHT = -1,
        LEFT = 1,
        STRAIGHT = 0
    };

/** \brief
     * Returns the orientation index of the direction of the point q relative to
     * a directed infinite line specified by p1-p2.
     *
     * The index indicates whether the point lies to the
     * `Orientation::LEFT` or `Orientation::RIGHT`
     * of the line, or lies on it `Orientation::COLLINEAR`.
     * The index also indicates the orientation of the triangle formed
     * by the three points
     * ( `Orientation::COUNTERCLOCKWISE`,
     * `Orientation::CLOCKWISE`, or `Orientation::STRAIGHT` )
    */
    static int index(const geom::Coordinate& p1, const geom::Coordinate& p2,
                     const geom::Coordinate& q);

/** \brief
     * Computes whether a ring defined by an array of
     * [Coordinates](@ref geom::Coordinate) is oriented counter-clockwise.
     *
     * - The list of points is assumed to have the first and last points equal.
     * - This will handle coordinate lists which contain repeated points.
     *
     * This algorithm is *only* guaranteed to work with valid rings. If the
     * ring is invalid (e.g. self-crosses or touches), the computed result may not
     * be correct.
     *
     * @param ring an array of Coordinates forming a ring
     * @return `true` if the ring is oriented counter-clockwise.
     * @throws IllegalArgumentException
     *           if there are too few points to determine orientation (&lt; 4)
    */
    static bool isCCW(const geom::CoordinateSequence* ring);

};

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

#endif // GEOS_ALGORITHM_ORIENTATION_H