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##### relation (with strategy)

Calculates the relation between a pair of geometries as defined in DE-9IM.

###### Synopsis

    template<typename Geometry1, typename Geometry2, typename Strategy>
    de9im::matrix relation(Geometry1 const & geometry1, Geometry2 const & geometry2, 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
Strategy const & | Any type fulfilling a Relation Strategy Concept | strategy | The strategy which will be used for relation calculations

###### Returns

The DE-9IM matrix expressing the relation between geometries.

###### Header

Either

`#include <boost/geometry.hpp>`

Or

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

###### Conformance

This function is additional and not described in the OGC standard. The spatial relation is represented by DE-9IM matrix.

###### Example

Shows how to calculate the spatial relation between a point and a polygon

    #include <iostream>
    #include <string>

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

    int main()
    {
        using point_type = boost::geometry::model::d2::point_xy<double>;
        using polygon_type = boost::geometry::model::polygon<point_type>;

        polygon_type poly;
        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);

        point_type p(4, 1);

        boost::geometry::de9im::matrix matrix = boost::geometry::relation(p, poly);
        std::string code = matrix.str();

        std::cout << "relation: " << code << std::endl;

        return 0;
    }

Output:

    relation: 0FFFFF212

###### See also

- de9im::matrix
- relate