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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(void)
    {
        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));

        // 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;
    }