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#### model::polygon

The polygon contains an outer ring and zero or more inner rings.

###### Model of

Polygon Concept

###### Synopsis

    template<typename Point, bool ClockWise, bool Closed, template< typename, typename > class PointList,
             template< typename, typename > class RingList, template< typename > class PointAlloc, template< typename > class RingAlloc>
    class model::polygon
    {
      // ...
    };

###### 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 PointList | std::vector | container type for points, for example std::vector, std::list, std::deque
template< typename, typename > class RingList | std::vector | container type for inner rings, for example std::vector, std::list, std::deque
template< typename > class PointAlloc | std::allocator | container-allocator-type, for the points
template< typename > class RingAlloc | std::allocator | container-allocator-type, for the rings

###### Constructor(s)

Function | Description | Parameters
--- | --- | ---

    polygon()

Default constructor, creating an empty polygon.

    polygon(std::initializer_list< ring_type > l)

Constructor taking std::initializer_list, filling the polygon.

std::initializer_list< ring_type >: l:

###### Member Function(s)

Function | Description | Parameters | Returns
--- | --- | --- | ---

    ring_type const & outer()

    inner_container_type const & inners()

    ring_type & outer()

    inner_container_type & inners()

    void clear()

Utility method, clears outer and inner rings.

###### Header

Either

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

Or

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

###### Examples

Declaration and use of the Boost.Geometry model::polygon, modelling the Polygon 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::polygon<point_t> polygon_t;

        polygon_t poly1;

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

        polygon_t polygon2{{{0.0, 0.0}, {0.0, 5.0}, {5.0, 5.0}, {5.0, 0.0}, {0.0, 0.0}},
                           {{1.0, 1.0}, {4.0, 1.0}, {4.0, 4.0}, {1.0, 4.0}, {1.0, 1.0}}};

    #endif

        bg::append(poly1.outer(), point_t(0.0, 0.0));
        bg::append(poly1.outer(), point_t(0.0, 5.0));
        bg::append(poly1.outer(), point_t(5.0, 5.0));
        bg::append(poly1.outer(), point_t(5.0, 0.0));
        bg::append(poly1.outer(), point_t(0.0, 0.0));

        poly1.inners().resize(1);
        bg::append(poly1.inners()[0], point_t(1.0, 1.0));
        bg::append(poly1.inners()[0], point_t(4.0, 1.0));
        bg::append(poly1.inners()[0], point_t(4.0, 4.0));
        bg::append(poly1.inners()[0], point_t(1.0, 4.0));
        bg::append(poly1.inners()[0], point_t(1.0, 1.0));

        double a = bg::area(poly1);

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

        return 0;
    }

| Default parameters, clockwise, closed polygon.
| Default-construct a polygon.
| Construct a polygon containing an exterior and interior ring, using C++11 unified initialization syntax.
| Append point to the exterior ring.
| Resize a container of interior rings.
| Append point to the interior ring.

Output:

    16