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Calculates the number of points of a geometry.
The free function num_points calculates the number of points of a geometry.
template<typename Geometry> std::size_t num_points(Geometry const & geometry, bool add_for_open = false)
| 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) | 
The calculated number of points
Either
          #include <boost/geometry.hpp>
        
Or
          #include <boost/geometry/algorithms/num_points.hpp>
        
The function num_points implements function NumPoints from the OGC Simple Feature Specification.
| ![[Note]](../../../../../../../doc/src/images/note.png) | Note | 
|---|---|
| num_points can be called for any geometry and not just linestrings (as the standard describes) | 
| 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 | 
Constant or Linear
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