text: // Boost.Geometry (aka GGL, Generic Geometry Library)
  
  // Copyright (c) 2007-2014 Barend Gehrels, Amsterdam, the Netherlands.
  // Copyright (c) 2008-2014 Bruno Lalande, Paris, France.
  // Copyright (c) 2009-2014 Mateusz Loskot, London, UK.
  
  // This file was modified by Oracle on 2014, 2015.
  // Modifications copyright (c) 2014-2015, Oracle and/or its affiliates.
  
  // Contributed and/or modified by Menelaos Karavelas, on behalf of Oracle
  // Contributed and/or modified by Adam Wulkiewicz, on behalf of Oracle
  
  // 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_ALGORITHMS_LENGTH_HPP
  #define BOOST_GEOMETRY_ALGORITHMS_LENGTH_HPP
  
  #include <iterator>
  
  #include <boost/concept_check.hpp>
  #include <boost/core/ignore_unused.hpp>
  #include <boost/mpl/fold.hpp>
  #include <boost/mpl/greater.hpp>
  #include <boost/mpl/if.hpp>
  #include <boost/mpl/insert.hpp>
  #include <boost/mpl/int.hpp>
  #include <boost/mpl/set.hpp>
  #include <boost/mpl/size.hpp>
  #include <boost/mpl/transform.hpp>
  #include <boost/range/begin.hpp>
  #include <boost/range/end.hpp>
  #include <boost/range/iterator.hpp>
  #include <boost/range/value_type.hpp>
  #include <boost/variant/apply_visitor.hpp>
  #include <boost/variant/static_visitor.hpp>
  #include <boost/variant/variant_fwd.hpp>
  
  #include <boost/geometry/core/cs.hpp>
  #include <boost/geometry/core/closure.hpp>
  #include <boost/geometry/core/tags.hpp>
  
  #include <boost/geometry/geometries/concepts/check.hpp>
  
  #include <boost/geometry/algorithms/assign.hpp>
  #include <boost/geometry/algorithms/detail/calculate_null.hpp>
  #include <boost/geometry/algorithms/detail/multi_sum.hpp>
  // #include <boost/geometry/algorithms/detail/throw_on_empty_input.hpp>
  #include <boost/geometry/views/closeable_view.hpp>
  #include <boost/geometry/strategies/default_strategy.hpp>
  #include <boost/geometry/strategies/distance.hpp>
  #include <boost/geometry/strategies/default_length_result.hpp>
  
  
  namespace boost { namespace geometry
  {
  
  
  #ifndef DOXYGEN_NO_DETAIL
  namespace detail { namespace length
  {
  
  
  template<typename Segment>
  struct segment_length
  {
      template <typename Strategy>
      static inline typename default_length_result<Segment>::type apply(
              Segment const& segment, Strategy const& strategy)
      {
          boost::ignore_unused(strategy);
          typedef typename point_type<Segment>::type point_type;
          point_type p1, p2;
          geometry::detail::assign_point_from_index<0>(segment, p1);
          geometry::detail::assign_point_from_index<1>(segment, p2);
          return strategy.apply(p1, p2);
      }
  };
  
  /*!
  \brief Internal, calculates length of a linestring using iterator pairs and
      specified strategy
  \note for_each could be used here, now that point_type is changed by boost
      range iterator
  */
  template<typename Range, closure_selector Closure>
  struct range_length
  {
      typedef typename default_length_result<Range>::type return_type;
  
      template <typename Strategy>
      static inline return_type apply(
              Range const& range, Strategy const& strategy)
      {
          boost::ignore_unused(strategy);
          typedef typename closeable_view<Range const, Closure>::type view_type;
          typedef typename boost::range_iterator
              <
                  view_type const
              >::type iterator_type;
  
          return_type sum = return_type();
          view_type view(range);
          iterator_type it = boost::begin(view), end = boost::end(view);
          if(it != end)
          {
              for(iterator_type previous = it++;
                      it != end;
                      ++previous, ++it)
              {
                  // Add point-point distance using the return type belonging
                  // to strategy
                  sum += strategy.apply(*previous, *it);
              }
          }
  
          return sum;
      }
  };
  
  
  }} // namespace detail::length
  #endif // DOXYGEN_NO_DETAIL
  
  
  #ifndef DOXYGEN_NO_DISPATCH
  namespace dispatch
  {
  
  
  template <typename Geometry, typename Tag = typename tag<Geometry>::type>
  struct length : detail::calculate_null
  {
      typedef typename default_length_result<Geometry>::type return_type;
  
      template <typename Strategy>
      static inline return_type apply(Geometry const& geometry, Strategy const& strategy)
      {
          return calculate_null::apply<return_type>(geometry, strategy);
      }
  };
  
  
  template <typename Geometry>
  struct length<Geometry, linestring_tag>
      : detail::length::range_length<Geometry, closed>
  {};
  
  
  // RING: length is currently 0; it might be argued that it is the "perimeter"
  
  
  template <typename Geometry>
  struct length<Geometry, segment_tag>
      : detail::length::segment_length<Geometry>
  {};
  
  
  template <typename MultiLinestring>
  struct length<MultiLinestring, multi_linestring_tag> : detail::multi_sum
  {
      template <typename Strategy>
      static inline typename default_length_result<MultiLinestring>::type
      apply(MultiLinestring const& multi, Strategy const& strategy)
      {
          return multi_sum::apply
                 <
                     typename default_length_result<MultiLinestring>::type,
                     detail::length::range_length
                     <
                         typename boost::range_value<MultiLinestring>::type,
                         closed // no need to close it explicitly
                     >
                 >(multi, strategy);
  
      }
  };
  
  
  } // namespace dispatch
  #endif // DOXYGEN_NO_DISPATCH
  
  
  namespace resolve_strategy {
  
  struct length
  {
      template <typename Geometry, typename Strategy>
      static inline typename default_length_result<Geometry>::type
      apply(Geometry const& geometry, Strategy const& strategy)
      {
          return dispatch::length<Geometry>::apply(geometry, strategy);
      }
  
      template <typename Geometry>
      static inline typename default_length_result<Geometry>::type
      apply(Geometry const& geometry, default_strategy)
      {
          typedef typename strategy::distance::services::default_strategy
              <
                  point_tag, point_tag, typename point_type<Geometry>::type
              >::type strategy_type;
  
          return dispatch::length<Geometry>::apply(geometry, strategy_type());
      }
  };
  
  } // namespace resolve_strategy
  
  
  namespace resolve_variant {
  
  template <typename Geometry>
  struct length
  {
      template <typename Strategy>
      static inline typename default_length_result<Geometry>::type
      apply(Geometry const& geometry, Strategy const& strategy)
      {
          return resolve_strategy::length::apply(geometry, strategy);
      }
  };
  
  template <BOOST_VARIANT_ENUM_PARAMS(typename T)>
  struct length<boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)> >
  {
      typedef typename default_length_result
          <
              boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>
          >::type result_type;
  
      template <typename Strategy>
      struct visitor
          : static_visitor<result_type>
      {
          Strategy const& m_strategy;
  
          visitor(Strategy const& strategy)
              : m_strategy(strategy)
          {}
  
          template <typename Geometry>
          inline typename default_length_result<Geometry>::type
          operator()(Geometry const& geometry) const
          {
              return length<Geometry>::apply(geometry, m_strategy);
          }
      };
  
      template <typename Strategy>
      static inline result_type apply(
          variant<BOOST_VARIANT_ENUM_PARAMS(T)> const& geometry,
          Strategy const& strategy
      )
      {
          return boost::apply_visitor(visitor<Strategy>(strategy), geometry);
      }
  };
  
  } // namespace resolve_variant
  
  
  /*!
  \brief \brief_calc{length}
  \ingroup length
  \details \details_calc{length, length (the sum of distances between consecutive points)}. \details_default_strategy
  \tparam Geometry \tparam_geometry
  \param geometry \param_geometry
  \return \return_calc{length}
  
  \qbk{[include reference/algorithms/length.qbk]}
  \qbk{[length] [length_output]}
   */
  template<typename Geometry>
  inline typename default_length_result<Geometry>::type
  length(Geometry const& geometry)
  {
      concepts::check<Geometry const>();
  
      // detail::throw_on_empty_input(geometry);
  
      return resolve_variant::length<Geometry>::apply(geometry, default_strategy());
  }
  
  
  /*!
  \brief \brief_calc{length} \brief_strategy
  \ingroup length
  \details \details_calc{length, length (the sum of distances between consecutive points)} \brief_strategy. \details_strategy_reasons
  \tparam Geometry \tparam_geometry
  \tparam Strategy \tparam_strategy{distance}
  \param geometry \param_geometry
  \param strategy \param_strategy{distance}
  \return \return_calc{length}
  
  \qbk{distinguish,with strategy}
  \qbk{[include reference/algorithms/length.qbk]}
  \qbk{[length_with_strategy] [length_with_strategy_output]}
   */
  template<typename Geometry, typename Strategy>
  inline typename default_length_result<Geometry>::type
  length(Geometry const& geometry, Strategy const& strategy)
  {
      concepts::check<Geometry const>();
  
      // detail::throw_on_empty_input(geometry);
  
      return resolve_variant::length<Geometry>::apply(geometry, strategy);
  }
  
  
  }} // namespace boost::geometry
  
  #endif // BOOST_GEOMETRY_ALGORITHMS_LENGTH_HPP
  