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##### touches (one geometry)

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

###### Synopsis

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

###### Parameters

Type | Concept | Name | Description
--- | --- | --- | ---
Geometry const & | Any type fulfilling a Geometry Concept | geometry | A model of the specified concept

###### 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;
    }

| Convenient namespace alias

Output:

    Touches: Yes

    Touches: No