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Calculates the centroid of a geometry.
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.
template<typename Geometry, typename Point> void centroid(Geometry const & geometry, Point & c)
| 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 | 
Either
            #include <boost/geometry.hpp>
          
Or
            #include <boost/geometry/algorithms/centroid.hpp>
          
The function centroid implements function Centroid from the OGC Simple Feature Specification.
| 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 | 
| 2D | 3D | |
|---|---|---|
| Point | 
                       | 
                       | 
| Segment | 
                       | 
                       | 
| Box | 
                       | 
                       | 
| Linestring | 
                       | 
                       | 
| Ring | 
                       | 
                       | 
| Polygon | 
                       | 
                       | 
| MultiPoint | 
                       | 
                       | 
| MultiLinestring | 
                       | 
                       | 
| MultiPolygon | 
                       | 
                       | 
Linear
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.