[/============================================================================
  Boost.Geometry (aka GGL, Generic Geometry Library)

  Copyright (c) 2009-2011 Mateusz Loskot, London, UK.
  Copyright (c) 2009-2011 Barend Gehrels, Amsterdam, the Netherlands.
  Copyright (c) 2009-2011 Bruno Lalande, Paris, France.

  Use, modification and distribution is subject to the Boost Software License,
  Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
  http://www.boost.org/LICENSE_1_0.txt)
=============================================================================/]

[section:concept_polygon Polygon Concept]

[heading Description]
[concept Polygon..polygon]

A polygon is ['A polygon is a planar surface defined by one exterior boundary and zero or more interior boundaries.] 
([@http://portal.opengeospatial.org/files/?artifact_id=25355 opengeospatial]).

So the definition of a Boost.Geometry polygon differs a bit from e.g. Wiki, where a polygon does not have holes. A
polygon of Boost.Geometry is a polygon with or without holes.
['(A polygon without holes is a ['helper geometry] within Boost.Geometry, and referred to as a ring.)]

[heading Concept Definition]

The Polygon Concept is defined as following:

* there must be a specialization of `traits::tag` defining `polygon_tag` as type
* there must be a specialization of `traits::ring_type` defining the type of its exterior ring and interior rings as type
* this type defined by `ring_type` must fulfill the [link geometry.reference.concepts.concept_ring Ring Concept]
* there must be a specialization of `traits::interior_type` defining the type of the collection of its interior rings as type;
    this collection itself must fulfill a Boost.Range Random Access Range Concept
* there must be a specialization of `traits::exterior_ring` with two functions named `get`, returning the exterior ring, one being const, the other being non const
* there must be a specialization of `traits::interior_rings` with two functions named `get`, returning the interior rings, one being const, the other being non const

[heading Available Models]	
* [link geometry.reference.models.model_polygon polygon]
* a Boost.Polygon polygon_with_holes_data (requires `#include boost/geometry/geometries/adapted/boost_polygon/polygon.hpp>`)

[endsect]
