Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

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union_

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

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

Collection &

output collection, either a multi-geometry, or a std::vector<Geometry> / std::deque<Geometry> etc

output_collection

the output collection

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] Note

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

Behavior

Case

Behavior

GeometryOut is a Point

Calculates union linestrings of input (multi)points

GeometryOut is a Linestring

Calculates union linestrings of input (multi)linestrings

GeometryOut is a Polygon

Calculates union polygons of input (multi)polygons and/or boxes

[Note] 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

union

See also

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