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#### model::ring

A ring (aka linear ring) is a closed line which should not be selfintersecting.

###### Model of

Ring Concept

###### Synopsis

    template<typename Point, bool ClockWise, bool Closed, template< typename, typename > class Container,
             template< typename > class Allocator>
    class model::ring
          : public Container< Point, Allocator< Point > >
    {
      // ...
    };

###### Template parameter(s)

Parameter | Default | Description
--- | --- | ---
typename Point |  | point type
bool ClockWise | true | true for clockwise direction, false for CounterClockWise direction
bool Closed | true | true for closed polygons (last point == first point), false open points
template< typename, typename > class Container | std::vector | container type, for example std::vector, std::deque
template< typename > class Allocator | std::allocator | container-allocator-type

###### Constructor(s)

Function | Description | Parameters
--- | --- | ---
    ring()
| Default constructor, creating an empty ring. |
    template<typename Iterator>
    ring(Iterator begin, Iterator end)
| Constructor with begin and end, filling the ring. | Iterator: begin: Iterator: end:
    ring(std::initializer_list< Point > l)
| Constructor taking std::initializer_list, filling the ring. | std::initializer_list< Point >: l:

###### Header

Either

`#include <boost/geometry/geometries/geometries.hpp>`

Or

`#include <boost/geometry/geometries/ring.hpp>`

###### Examples

Declaration and use of the Boost.Geometry model::ring, modelling the Ring Concept

    #include <iostream>
    #include <boost/geometry.hpp>
    #include <boost/geometry/geometries/geometries.hpp>

    namespace bg = boost::geometry;

    int main()
    {
        typedef bg::model::point<double, 2, bg::cs::cartesian> point_t;
        typedef bg::model::ring<point_t> ring_t;

        ring_t ring1;

    #if !defined(BOOST_NO_CXX11_UNIFIED_INITIALIZATION_SYNTAX) \
     && !defined(BOOST_NO_CXX11_HDR_INITIALIZER_LIST)

        ring_t ring2{{0.0, 0.0}, {0.0, 5.0}, {5.0, 5.0}, {5.0, 0.0}, {0.0, 0.0}};

    #endif

        bg::append(ring1, point_t(0.0, 0.0));
        bg::append(ring1, point_t(0.0, 5.0));
        bg::append(ring1, point_t(5.0, 5.0));
        bg::append(ring1, point_t(5.0, 0.0));
        bg::append(ring1, point_t(0.0, 0.0));

        double a = bg::area(ring1);

        std::cout << a << std::endl;

        return 0;
    }

| Default parameters, clockwise, closed ring.
| Default-construct a ring.
| Construct a ring containing four points plus one closing point, using C++11 unified initialization syntax.
| Append point.

Output:

    25