centroid

Calculates the centroid of a geometry.

Description

The free function centroid calculates the geometric center (or: center of mass) of a geometry. It uses the default strategy, based on the coordinate system of the geometry.

Synopsis

template<typename Geometry, typename Point>
void centroid(Geometry const & geometry, Point & c)

Parameters

Type	Concept	Name	Description
Geometry const &	Any type fulfilling a Geometry Concept	geometry	A model of the specified concept
Point &	Any type fulfilling a Point Concept	c	The calculated centroid will be assigned to this point reference

Header

Either

#include <boost/geometry.hpp>

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

Conformance

The function centroid implements function Centroid from the OGC Simple Feature Specification.

Behavior

Case	Behavior
Point	Returns the point itself as the centroid
Multi Point	Calculates centroid (based on average)
linear (e.g. linestring)	Calculates centroid (based on weighted length)
areal (e.g. polygon)	Calculates centroid
Empty (e.g. polygon without points)	Throws a centroid_exception
Cartesian	Implemented
Spherical	Calculates the centroid as if based on Cartesian coordinates

Supported geometries

	2D	3D
Point
Segment
Box
Linestring
Ring
Polygon
MultiPoint
MultiLinestring
MultiPolygon

Complexity

Linear

Example

Shows calculation of a centroid of a polygon

#include <iostream>
#include <list>

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


int main()
{
    typedef boost::geometry::model::d2::point_xy<double> point_type;
    typedef boost::geometry::model::polygon<point_type> polygon_type;

    polygon_type poly;
    boost::geometry::read_wkt(
        "POLYGON((2 1.3,2.4 1.7,2.8 1.8,3.4 1.2,3.7 1.6,3.4 2,4.1 3,5.3 2.6,5.4 1.2,4.9 0.8,2.9 0.7,2 1.3)"
            "(4.0 2.0, 4.2 1.4, 4.8 1.9, 4.4 2.2, 4.0 2.0))", poly);

    point_type p;
    boost::geometry::centroid(poly, p);

    std::cout << "centroid: " << boost::geometry::dsv(p) << std::endl;

    return 0;
}

Output:

centroid: (4.04663, 1.6349)

Note that the centroid might be located in a hole or outside a polygon, easily.