num_interior_rings

Calculates the number of interior rings of a geometry.

Description

The free function num_interior_rings calculates the number of interior rings of a geometry.

Synopsis

template<typename Geometry>
std::size_t num_interior_rings(Geometry const & geometry)

Parameters

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

Returns

The calculated number of interior rings

Header

Either

#include <boost/geometry.hpp>

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

Conformance

The function num_interior_ring implements function NumInteriorRing from the OGC Simple Feature Specification.

	Note
	Boost.Geometry adds an "s"

Behavior

Case	Behavior
Polygon	Returns the number of its interior rings
Multi Polygon	Returns the number of the interior rings of all polygons
Other geometries	Returns 0

Complexity

Constant

Examples

Get the number of interior rings in a multi-polygon

#include <iostream>

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


int main()
{
    boost::geometry::model::multi_polygon
        <
            boost::geometry::model::polygon
                <
                    boost::geometry::model::d2::point_xy<double>
                >
        > mp;
    boost::geometry::read_wkt("MULTIPOLYGON(((0 0,0 10,10 0,0 0),(1 1,1 9,9 1,1 1)),((10 10,10 7,7 10,10 10)))", mp);
    std::cout << "Number of interior rings: " << boost::geometry::num_interior_rings(mp) << std::endl;

    return 0;
}

Output:

Number of interior rings: 1