Boost C++ Libraries

Metafunction defining value as the point order (clockwise, counterclockwise) of the specified geometry type.

Synopsis

template<typename Geometry>
struct point_order
      : public std::integral_constant< order_selector, core_dispatch::point_order< tag_t< Geometry >, util::remove_cptrref_t< Geometry > >::value >
{
  // ...
};

Template parameter(s)

Header

Either

#include <boost/geometry.hpp>

Or

#include <boost/geometry/core/point_order.hpp>

	Note
	The point order is defined for any geometry type, but only has a real meaning for areal geometry types (ring, polygon, multi_polygon)

Complexity

Compile time

Example

Examine the expected point order of a polygon type

#include <iostream>

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

int main()
{
    using point_type = boost::geometry::model::d2::point_xy<double>;
    using polygon_type = boost::geometry::model::polygon<point_type, false>;

    boost::geometry::order_selector order = boost::geometry::point_order<polygon_type>::value;

    std::cout << "order: " << order << std::endl
        << "(clockwise = " << boost::geometry::clockwise
        << ", counterclockwise = " << boost::geometry::counterclockwise
        << ") "<< std::endl;

    return 0;
}

Output:

order: 2
(clockwise = 1, counterclockwise = 2)

See also