sym_difference

Calculate the symmetric difference of two geometries.

Description

The free function symmetric difference calculates the spatial set theoretic symmetric difference (XOR) of two geometries.

Synopsis

template<typename Geometry1, typename Geometry2, typename Collection>
void sym_difference(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>

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

Conformance

The function sym_difference implements function SymDifference from the OGC Simple Feature Specification.

Behavior

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

Example

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

Boost C++ Libraries