EVOLUTION-MANAGER

Edit File: CascadedPolygonUnion.h

/**********************************************************************
 *
 * GEOS - Geometry Engine Open Source
 * http://geos.osgeo.org
 *
 * Copyright (C) 2011 Sandro Santilli <strk@kbt.io>
 * Copyright (C) 2006 Refractions Research 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.
 *
 **********************************************************************
 *
 * Last port: operation/union/CascadedPolygonUnion.java r487 (JTS-1.12+)
 * Includes custom code to deal with https://trac.osgeo.org/geos/ticket/837
 *
 **********************************************************************/

#ifndef GEOS_OP_UNION_CASCADEDPOLYGONUNION_H
#define GEOS_OP_UNION_CASCADEDPOLYGONUNION_H

#include <geos/export.h>

#include <vector>
#include <algorithm>
#include <memory>

#include "GeometryListHolder.h"

// Forward declarations
namespace geos {
namespace geom {
class GeometryFactory;
class Geometry;
class Polygon;
class MultiPolygon;
class Envelope;
}
namespace index {
namespace strtree {
class ItemsList;
}
}
}

namespace geos {
namespace operation { // geos::operation
namespace geounion {  // geos::operation::geounion

/**
 * \brief
 * Provides an efficient method of unioning a collection of polygonal geometries.
 *
 * This algorithm is faster and likely more robust than the simple iterated
 * approach of repeatedly unioning each polygon to a result geometry.
 *
 * The `buffer(0)` trick is sometimes faster, but can be less robust and
 * can sometimes take an exceptionally long time to complete.
 * This is particularly the case where there is a high degree of overlap
 * between the polygons.  In this case, `buffer(0)` is forced to compute
 * with *all* line segments from the outset, whereas cascading can eliminate
 * many segments at each stage of processing.
 * The best case for buffer(0) is the trivial case where there is `no` overlap
 * between the input geometries. However, this case is likely rare in practice.
 */
class GEOS_DLL CascadedPolygonUnion {
private:
    std::vector<geom::Polygon*>* inputPolys;
    geom::GeometryFactory const* geomFactory;

/**
     * The effectiveness of the index is somewhat sensitive
     * to the node capacity.
     * Testing indicates that a smaller capacity is better.
     * For an STRtree, 4 is probably a good number (since
     * this produces 2x2 "squares").
     */
    static int const STRTREE_NODE_CAPACITY = 4;

/** \brief
     * Computes a [Geometry](@ref geom::Geometry) containing only polygonal components.
     *
     * Extracts the [Polygons](@ref geom::Polygon) from the input
     * and returns them as an appropriate polygonal geometry.
     *
     * If the input is already `Polygonal`, it is returned unchanged.
     *
     * A particular use case is to filter out non-polygonal components
     * returned from an overlay operation.
     *
     * @param g the geometry to filter
     * @return a Polygonal geometry
     */
    static std::unique_ptr<geom::Geometry> restrictToPolygons(std::unique_ptr<geom::Geometry> g);

public:
    CascadedPolygonUnion();

/** \brief
     * Computes the union of a collection of polygonal [Geometrys](@ref geom::Geometry).
     *
     * @param polys a collection of polygonal [Geometrys](@ref geom::Geometry).
     *              ownership of elements *and* vector are left to caller.
     */
    static geom::Geometry* Union(std::vector<geom::Polygon*>* polys);

/** \brief
     * Computes the union of a set of polygonal [Geometrys](@ref geom::Geometry).
     *
     * @tparam T an iterator yelding something castable to const Polygon *
     * @param start start iterator
     * @param end end iterator
     */
    template <class T>
    static geom::Geometry*
    Union(T start, T end)
    {
        std::vector<geom::Polygon*> polys;
        for(T i = start; i != end; ++i) {
            const geom::Polygon* p = dynamic_cast<const geom::Polygon*>(*i);
            polys.push_back(const_cast<geom::Polygon*>(p));
        }
        return Union(&polys);
    }

/** \brief
     * Computes the union of a collection of polygonal [Geometrys](@ref geom::Geometry).
     *
     * @param polys a collection of polygonal [Geometrys](@ref geom::Geometry).
     *              Ownership of elements *and* vector are left to caller.
     */
    static geom::Geometry* Union(const geom::MultiPolygon* polys);

/** \brief
     * Creates a new instance to union the given collection of
     * [Geometrys](@ref geom::Geometry).
     *
     * @param polys a collection of polygonal [Geometrys](@ref geom::Geometry).
     *              Ownership of elements *and* vector are left to caller.
     */
    CascadedPolygonUnion(std::vector<geom::Polygon*>* polys)
        : inputPolys(polys),
          geomFactory(nullptr)
    {}

/** \brief
     * Computes the union of the input geometries.
     *
     * @return the union of the input geometries
     * @return `null` if no input geometries were provided
     */
    geom::Geometry* Union();

private:
    geom::Geometry* unionTree(index::strtree::ItemsList* geomTree);

/**
     * Unions a list of geometries
     * by treating the list as a flattened binary tree,
     * and performing a cascaded union on the tree.
     */
    geom::Geometry* binaryUnion(GeometryListHolder* geoms);

/**
     * Unions a section of a list using a recursive binary union on each half
     * of the section.
     *
     * @param geoms the list of geometries containing the section to union
     * @param start the start index of the section
     * @param end the index after the end of the section
     * @return the union of the list section
     */
    geom::Geometry* binaryUnion(GeometryListHolder* geoms, std::size_t start,
                                std::size_t end);

/**
     * Reduces a tree of geometries to a list of geometries
     * by recursively unioning the subtrees in the list.
     *
     * @param geomTree a tree-structured list of geometries
     * @return a list of Geometrys
     */
    GeometryListHolder* reduceToGeometries(index::strtree::ItemsList* geomTree);

/**
     * Computes the union of two geometries,
     * either of both of which may be null.
     *
     * @param g0 a Geometry
     * @param g1 a Geometry
     * @return the union of the input(s)
     * @return null if both inputs are null
     */
    geom::Geometry* unionSafe(geom::Geometry* g0, geom::Geometry* g1);

/**
     * Encapsulates the actual unioning of two polygonal geometries.
     *
     * @param g0
     * @param g1
     * @return
     */
    static geom::Geometry* unionActual(geom::Geometry* g0, geom::Geometry* g1);
};

} // namespace geos::operation::union
} // namespace geos::operation
} // namespace geos

#endif