difference (with strategy)

Description

Calculate the difference of two geometries

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

Synopsis

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

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
Strategy const &	Any type fulfilling a Difference Strategy Concept	strategy	The strategy which will be used for difference calculations

Header

Either

#include <boost/geometry.hpp>

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

Conformance

The function difference implements function Difference 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 subtract one polygon from another polygon

#include <iostream>
#include <list>

#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::list<polygon> output;
    boost::geometry::difference(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;
    }


    output.clear();
    boost::geometry::difference(blue, green, output);

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


    return 0;
}

Output:

green - blue:
0: 0.02375
1: 0.542951
2: 0.0149697
3: 0.226855
4: 0.839424



blue - green:
0: 0.525154
1: 0.015
2: 0.181136
3: 0.128798
4: 0.340083
5: 0.307778