text: // Boost.Geometry (aka GGL, Generic Geometry Library)
  
  // Copyright (c) 2007-2012 Barend Gehrels, Amsterdam, the Netherlands.
  // Copyright (c) 2008-2012 Bruno Lalande, Paris, France.
  // Copyright (c) 2009-2012 Mateusz Loskot, London, UK.
  
  // Parts of Boost.Geometry are redesigned from Geodan's Geographic Library
  // (geolib/GGL), copyright (c) 1995-2010 Geodan, Amsterdam, the Netherlands.
  
  // 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)
  
  #ifndef BOOST_GEOMETRY_MULTI_ALGORITHMS_CENTROID_HPP
  #define BOOST_GEOMETRY_MULTI_ALGORITHMS_CENTROID_HPP
  
  
  #include <boost/range.hpp>
  
  #include <boost/geometry/algorithms/centroid.hpp>
  #include <boost/geometry/multi/core/tags.hpp>
  #include <boost/geometry/multi/core/point_type.hpp>
  #include <boost/geometry/multi/geometries/concepts/check.hpp>
  #include <boost/geometry/multi/algorithms/num_points.hpp>
  
  
  namespace boost { namespace geometry
  {
  
  
  #ifndef DOXYGEN_NO_DETAIL
  namespace detail { namespace centroid
  {
  
  
  /*!
      \brief Building block of a multi-point, to be used as Policy in the
          more generec centroid_multi
  */
  struct centroid_multi_point_state
  {
      template <typename Point, typename Strategy>
      static inline void apply(Point const& point,
              Strategy const& strategy, typename Strategy::state_type& state)
      {
          strategy.apply(point, state);
      }
  };
  
  
  
  /*!
      \brief Generic implementation which calls a policy to calculate the
          centroid of the total of its single-geometries
      \details The Policy is, in general, the single-version, with state. So
          detail::centroid::centroid_polygon_state is used as a policy for this
          detail::centroid::centroid_multi
  
  */
  template <typename Policy>
  struct centroid_multi
  {
      template <typename Multi, typename Point, typename Strategy>
      static inline void apply(Multi const& multi, Point& centroid,
              Strategy const& strategy)
      {
  #if ! defined(BOOST_GEOMETRY_CENTROID_NO_THROW)
          // If there is nothing in any of the ranges, it is not possible
          // to calculate the centroid
          if (geometry::num_points(multi) == 0)
          {
              throw centroid_exception();
          }
  #endif
  
          typename Strategy::state_type state;
  
          for (typename boost::range_iterator<Multi const>::type
                  it = boost::begin(multi);
              it != boost::end(multi);
              ++it)
          {
              Policy::apply(*it, strategy, state);
          }
          Strategy::result(state, centroid);
      }
  };
  
  
  
  }} // namespace detail::centroid
  #endif // DOXYGEN_NO_DETAIL
  
  
  
  #ifndef DOXYGEN_NO_DISPATCH
  namespace dispatch
  {
  
  template <typename MultiLinestring>
  struct centroid<MultiLinestring, multi_linestring_tag>
      : detail::centroid::centroid_multi
          <
              detail::centroid::centroid_range_state<closed>
          >
  {};
  
  template <typename MultiPolygon>
  struct centroid<MultiPolygon, multi_polygon_tag>
      : detail::centroid::centroid_multi
          <
              detail::centroid::centroid_polygon_state
          >
  {};
  
  
  template <typename MultiPoint>
  struct centroid<MultiPoint, multi_point_tag>
      : detail::centroid::centroid_multi
          <
              detail::centroid::centroid_multi_point_state
          >
  {};
  
  
  } // namespace dispatch
  #endif
  
  
  }} // namespace boost::geometry
  
  
  #endif // BOOST_GEOMETRY_MULTI_ALGORITHMS_CENTROID_HPP
  
  