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Calculate the symmetric difference of two geometries.
The free function symmetric difference calculates the spatial set theoretic symmetric difference (XOR) of two geometries.
template<typename Geometry1, typename Geometry2, typename Collection> void sym_difference(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/sym_difference.hpp>
          
The function sym_difference implements function SymDifference from the OGC Simple Feature Specification.
| Case | Behavior | 
|---|---|
| areal (e.g. polygon) | All combinations of: box, ring, polygon, multi_polygon | 
| linear (e.g. linestring) / areal (e.g. polygon) | A combinations of a (multi) linestring with a (multi) polygon results in a collection of linestrings | 
| linear (e.g. linestring) | All combinations of: linestring, multi_linestring; results in a collection of linestrings | 
| pointlike (e.g. point) | All combinations of: point, multi_point; results in a collection of points | 
| Other geometries | Not yet supported in this version | 
| Spherical | Not yet supported in this version | 
| Three dimensional | Not yet supported in this version | 
| ![[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 calculate the symmetric difference (XOR) of two polygons
#include <iostream> #include <boost/geometry.hpp> #include <boost/geometry/geometries/polygon.hpp> #include <boost/geometry/geometries/point_xy.hpp> #include <boost/geometry/geometries/multi_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); boost::geometry::model::multi_polygon<polygon> multi; boost::geometry::sym_difference(green, blue, multi); std::cout << "green XOR blue:" << std::endl << "total: " << boost::geometry::area(multi) << std::endl; int i = 0; BOOST_FOREACH(polygon const& p, multi) { std::cout << i++ << ": " << boost::geometry::area(p) << std::endl; } return 0; }
Output:
green XOR blue: total: 3.1459 0: 0.02375 1: 0.542951 2: 0.0149697 3: 0.226855 4: 0.839424 5: 0.525154 6: 0.015 7: 0.181136 8: 0.128798 9: 0.340083 10: 0.307778