Boost C++ Libraries

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difference

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>
void 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>

Or

#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] 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

difference_a

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

difference_b
See also

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