Boost C++ Libraries

Checks if a geometry has at least one touching point (self-tangency)

Synopsis

template<typename Geometry>
bool touches(Geometry const & geometry)

Parameters

Returns

Returns true if the geometry is self-touching

Header

Either

#include <boost/geometry.hpp>

Or

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

Conformance

The function touches implements function Touches from the OGC Simple Feature Specification.

The version with one parameter is additional and not described in the OGC standard

	Note
	Implemented for Point/Linestring/MultiLinestring/Polygon/MultiPolygon.

Examples

Checks if a geometry has at least one touching point (self-tangency)

#include <iostream>

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/polygon.hpp>

namespace bg = boost::geometry; 

int main()
{
    // Checks if the geometry has self-tangency.
    bg::model::polygon<bg::model::d2::point_xy<double> > poly1;
    bg::read_wkt("POLYGON((0 0,0 3,2 3,2 2,1 2,1 1,2 1,2 2,3 2,3 0,0 0))", poly1);
    bool check_touches = bg::touches(poly1);
    if (check_touches) {
         std::cout << "Touches: Yes" << std::endl;
    } else {
        std::cout << "Touches: No" << std::endl;
    }

    bg::model::polygon<bg::model::d2::point_xy<double> > poly2;
    bg::read_wkt("POLYGON((0 0,0 4,4 4,4 0,2 3,0 0))", poly2);
    check_touches = bg::touches(poly2);
    if (check_touches) {
         std::cout << "Touches: Yes" << std::endl;
    } else {
        std::cout << "Touches: No" << std::endl;
    }

    return 0;
}

Output:

Touches: Yes



Touches: No