num_points

Calculates the number of points of a geometry.

Description

The free function num_points calculates the number of points of a geometry.

Synopsis

template<typename Geometry>
std::size_t num_points(Geometry const & geometry, bool add_for_open = false)

Parameters

Type	Concept	Name	Description
Geometry const &	Any type fulfilling a Geometry Concept	geometry	A model of the specified concept
bool		add_for_open	add one for open geometries (i.e. polygon types which are not closed)

Returns

The calculated number of points

Header

Either

#include <boost/geometry.hpp>

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

Conformance

The function num_points implements function NumPoints from the OGC Simple Feature Specification.

	Note
	num_points can be called for any geometry and not just linestrings (as the standard describes)

Behavior

Case	Behavior
Point	Returns 1
Segment	Returns 2
Box	Returns 2^d, where d is the dimension of the box
Rangelike (linestring, ring)	Returns boost::size(geometry)
Other geometries	Returns the sum of the number of points of its elements
Open geometries	Returns the sum of the number of points of its elements, it adds one for open (per ring) if specified
Closed geometries	Returns the sum of the number of points of its elements

Complexity

Constant or Linear

Examples

Get the number of points in a geometry

#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 points: " << boost::geometry::num_points(mp) << std::endl;

    return 0;
}

Output:

Number of points: 12