Boost C++ Libraries

Combines two geometries which each other.

Description

The free function union calculates the spatial set theoretic union of two geometries.

Synopsis

template<typename Geometry1, typename Geometry2, typename Collection>
void union_(Geometry1 const & geometry1, Geometry2 const & geometry2, Collection & output_collection)

Parameters

Header

Either

#include <boost/geometry.hpp>

Or

#include <boost/geometry/algorithms/union.hpp>

Conformance

The function union implements function Union from the OGC Simple Feature Specification.

	Note
	Boost.Geometry adds an underscore to avoid using the union keyword

Behavior

	Note
	Check the Polygon Concept for the rules that polygon input for this algorithm should fulfill

Example

Shows how to get a united geometry of two polygons

#include <iostream>
#include <vector>

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

#include <boost/foreach.hpp>


int main()
{
    typedef boost::geometry::model::polygon<boost::geometry::model::d2::point_xy<double> > polygon;

    polygon green, blue;

    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))", green);

    boost::geometry::read_wkt(
        "POLYGON((4.0 -0.5 , 3.5 1.0 , 2.0 1.5 , 3.5 2.0 , 4.0 3.5 , 4.5 2.0 , 6.0 1.5 , 4.5 1.0 , 4.0 -0.5))", blue);

    std::vector<polygon> output;
    boost::geometry::union_(green, blue, output);

    int i = 0;
    std::cout << "green || blue:" << std::endl;
    BOOST_FOREACH(polygon const& p, output)
    {
        std::cout << i++ << ": " << boost::geometry::area(p) << std::endl;
    }


    return 0;
}

Output:

green || blue:
0: 5.64795

See also