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##### closest_points (with strategy)

Calculate the closest points between two geometries using the specified strategy.

###### Description

The free function closest_points calculates the distance between two geometries using the specified strategy. Reasons to specify a strategy include: use another coordinate system for calculations; construct the strategy beforehand (e.g. with the radius of the Earth); select a strategy when there are more than one available for a calculation.

###### Synopsis

    template<typename Geometry1, typename Geometry2, typename Segment, typename Strategy>
    void closest_points(Geometry1 const & geometry1, Geometry2 const & geometry2, Segment & shortest_seg,
                        Strategy const & strategy)

###### Parameters

Type | Concept | Name | Description
--- | --- | --- | ---
Geometry1 const & | Any type fulfilling a Geometry Concept | geometry1 | A model of the specified concept
Geometry2 const & | Any type fulfilling a Geometry Concept | geometry2 | A model of the specified concept
Segment & | Any type fulfilling a Segment Concept | shortest_seg | Output segment containing the closest points
Strategy const & | Any type fulfilling a Closest Points Strategy Concept | strategy | The strategy which will be used for closest_points calculations

###### Header

Either

`#include <boost/geometry.hpp>`

Or

`#include <boost/geometry/algorithms/closest_points.hpp>`

###### Example

Shows calculation of the two closest points between two geometries using strategies

    #include <iostream>

    #include <boost/geometry.hpp>
    #include <boost/geometry/geometries/linestring.hpp>
    #include <boost/geometry/geometries/point_xy.hpp>
    #include <boost/geometry/geometries/polygon.hpp>
    #include <boost/geometry/geometries/multi_point.hpp>

    int main()
    {
        typedef boost::geometry::model::d2::point_xy
            <
                double,
                boost::geometry::cs::geographic<boost::geometry::degree>
            > point_type;
        typedef boost::geometry::model::polygon<point_type> polygon_type;
        typedef boost::geometry::model::linestring<point_type> linestring_type;
        typedef boost::geometry::model::multi_point<point_type> multi_point_type;

        point_type p(4.3,1.9);
        polygon_type poly;
        linestring_type line;
        multi_point_type mp;

        boost::geometry::strategies::closest_points::geographic<> strategies
            (boost::geometry::srs::spheroid<double>(6378137.0, 6356752.3142451793));

        boost::geometry::read_wkt(
            "POLYGON((2 1.3,2.4 1.7,2.8 1.8,3.4 1.2,3.7 1.6,3.4 2,4.1 3,5.3 2.6,5.4 1.2,4.9 0.8,2.9 0.7,2 1.3)"
                "(4.0 2.0, 4.2 1.4, 4.8 1.9, 4.4 2.2, 4.0 2.0))", poly);

        line.push_back(point_type(5,0));
        line.push_back(point_type(2,0));
        mp.push_back(point_type(2,0.5));
        mp.push_back(point_type(2,3));

        boost::geometry::model::segment<point_type> sout1,sout2,sout3;

        boost::geometry::closest_points(p, poly, sout1, strategies);
        std::cout << "Point-Poly: " << boost::geometry::wkt(sout1) << std::endl;

        boost::geometry::closest_points(poly, line, sout2, strategies);
        std::cout << "Poly-Line: " << boost::geometry::wkt(sout2) << std::endl;

        boost::geometry::closest_points(p, mp, sout3, strategies);
        std::cout << "Poly-MultiPoint: " << boost::geometry::wkt(sout3) << std::endl;

        return 0;
    }

Output:

    Point-Poly: LINESTRING(4.3 1.9,4.20096 2.1005)
    Poly-Line: LINESTRING(2.9 0.7,2.9 0)
    Poly-MultiPoint: LINESTRING(4.3 1.9,2 3)

###### See also

- distance