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Combines two geometries which each other.
The free function union calculates the spatial set theoretic union of two geometries.
template<typename Geometry1, typename Geometry2, typename Collection> void union_(Geometry1 const & geometry1, Geometry2 const & geometry2, Collection & output_collection)
| 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 | 
Either
          #include <boost/geometry.hpp>
        
Or
          #include <boost/geometry/algorithms/union.hpp>
        
The function union implements function Union from the OGC Simple Feature Specification.
| ![[Note]](../../../../../../../doc/src/images/note.png) | Note | 
|---|---|
| 
            Boost.Geometry adds an underscore to avoid using the  | 
| 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]](../../../../../../../doc/src/images/note.png) | Note | 
|---|---|
| Check the Polygon Concept for the rules that polygon input for this algorithm should fulfill | 
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