Index of shared pointers to polygons

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#### Index of shared pointers to polygons

    #include <boost/geometry.hpp>
    #include <boost/geometry/geometries/point.hpp>
    #include <boost/geometry/geometries/box.hpp>
    #include <boost/geometry/geometries/polygon.hpp>

    #include <boost/geometry/index/rtree.hpp>

    #include <cmath>
    #include <vector>
    #include <iostream>
    #include <boost/foreach.hpp>
    #include <boost/shared_ptr.hpp>

    namespace bg = boost::geometry;
    namespace bgi = boost::geometry::index;

    int main()
    {
        typedef bg::model::point<float, 2, bg::cs::cartesian> point;
        typedef bg::model::box<point> box;
        typedef bg::model::polygon<point, false, false> polygon; // ccw, open polygon
        typedef boost::shared_ptr<polygon> shp;
        typedef std::pair<box, shp> value;

        // create the rtree using default constructor
        bgi::rtree< value, bgi::linear<16, 4> > rtree;

        std::cout << "filling index with polygons shared pointers:" << std::endl;

        // create some polygons and fill the spatial index
        for ( unsigned i = 0 ; i < 10 ; ++i )
        {
            // create a polygon
            shp p(new polygon());
            for ( float a = 0 ; a < 6.28316f ; a += 1.04720f )
            {
                float x = i + int(10*::cos(a))*0.1f;
                float y = i + int(10*::sin(a))*0.1f;
                p->outer().push_back(point(x, y));
            }

            // display new polygon
            std::cout << bg::wkt<polygon>(*p) << std::endl;

            // calculate polygon bounding box
            box b = bg::return_envelope<box>(*p);
            // insert new value
            rtree.insert(std::make_pair(b, p));
        }

        // find values intersecting some area defined by a box
        box query_box(point(0, 0), point(5, 5));
        std::vector<value> result_s;
        rtree.query(bgi::intersects(query_box), std::back_inserter(result_s));

        // find 5 nearest values to a point
        std::vector<value> result_n;
        rtree.query(bgi::nearest(point(0, 0), 5), std::back_inserter(result_n));

        // note: in Boost.Geometry the WKT representation of a box is polygon

        // note: the values store the bounding boxes of polygons
        // the polygons aren't used for querying but are printed

        // display results
        std::cout << "spatial query box:" << std::endl;
        std::cout << bg::wkt<box>(query_box) << std::endl;
        std::cout << "spatial query result:" << std::endl;
        BOOST_FOREACH(value const& v, result_s)
            std::cout << bg::wkt<polygon>(*v.second) << std::endl;

        std::cout << "knn query point:" << std::endl;
        std::cout << bg::wkt<point>(point(0, 0)) << std::endl;
        std::cout << "knn query result:" << std::endl;
        BOOST_FOREACH(value const& v, result_n)
            std::cout << bg::wkt<polygon>(*v.second) << std::endl;

        return 0;
    }

##### Expected results

    filling index with polygons shared pointers:
    POLYGON((1 0,0.4 0.8,-0.5 0.8,-0.9 0,-0.4 -0.8,0.5 -0.8,1 0))
    POLYGON((2 1,1.4 1.8,0.5 1.8,0.1 1,0.6 0.2,1.5 0.2,2 1))
    POLYGON((3 2,2.4 2.8,1.5 2.8,1.1 2,1.6 1.2,2.5 1.2,3 2))
    POLYGON((4 3,3.4 3.8,2.5 3.8,2.1 3,2.6 2.2,3.5 2.2,4 3))
    POLYGON((5 4,4.4 4.8,3.5 4.8,3.1 4,3.6 3.2,4.5 3.2,5 4))
    POLYGON((6 5,5.4 5.8,4.5 5.8,4.1 5,4.6 4.2,5.5 4.2,6 5))
    POLYGON((7 6,6.4 6.8,5.5 6.8,5.1 6,5.6 5.2,6.5 5.2,7 6))
    POLYGON((8 7,7.4 7.8,6.5 7.8,6.1 7,6.6 6.2,7.5 6.2,8 7))
    POLYGON((9 8,8.4 8.8,7.5 8.8,7.1 8,7.6 7.2,8.5 7.2,9 8))
    POLYGON((10 9,9.4 9.8,8.5 9.8,8.1 9,8.6 8.2,9.5 8.2,10 9))
    spatial query box:
    POLYGON((0 0,0 5,5 5,5 0,0 0))
    spatial query result:
    POLYGON((1 0,0.4 0.8,-0.5 0.8,-0.9 0,-0.4 -0.8,0.5 -0.8,1 0))
    POLYGON((2 1,1.4 1.8,0.5 1.8,0.1 1,0.6 0.2,1.5 0.2,2 1))
    POLYGON((3 2,2.4 2.8,1.5 2.8,1.1 2,1.6 1.2,2.5 1.2,3 2))
    POLYGON((4 3,3.4 3.8,2.5 3.8,2.1 3,2.6 2.2,3.5 2.2,4 3))
    POLYGON((5 4,4.4 4.8,3.5 4.8,3.1 4,3.6 3.2,4.5 3.2,5 4))
    POLYGON((6 5,5.4 5.8,4.5 5.8,4.1 5,4.6 4.2,5.5 4.2,6 5))
    knn query point:
    POINT(0 0)
    knn query result:
    POLYGON((5 4,4.4 4.8,3.5 4.8,3.1 4,3.6 3.2,4.5 3.2,5 4))
    POLYGON((4 3,3.4 3.8,2.5 3.8,2.1 3,2.6 2.2,3.5 2.2,4 3))
    POLYGON((3 2,2.4 2.8,1.5 2.8,1.1 2,1.6 1.2,2.5 1.2,3 2))
    POLYGON((1 0,0.4 0.8,-0.5 0.8,-0.9 0,-0.4 -0.8,0.5 -0.8,1 0))
    POLYGON((2 1,1.4 1.8,0.5 1.8,0.1 1,0.6 0.2,1.5 0.2,2 1))