Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

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num_geometries

Calculates the number of geometries of a geometry.

Description

The free function num_geometries calculates the number of geometries of a geometry.

Synopsis

template<typename Geometry>
std::size_t num_geometries(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 geometries

Header

Either

#include <boost/geometry/geometry.hpp>

Or

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

Conformance

The function num_geometries implements function NumGeometries from the OGC Simple Feature Specification.

Behavior

Case

Behavior

single (e.g. point, polygon)

Returns 1

multiple (e.g. multi_point, multi_polygon)

Returns boost::size(geometry); the input is considered as a range

Complexity

Constant

Examples

Get the number of geometries making up a multi-geometry

#include <iostream>

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/polygon.hpp>
#include <boost/geometry/multi/geometries/multi_polygon.hpp>
#include <boost/geometry/io/wkt/wkt.hpp>
#include <boost/geometry/multi/io/wkt/wkt.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 geometries: " << boost::geometry::num_geometries(mp) << std::endl;

    return 0;
}

Output:

Number of geometries: 2

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