Chris@16: // Boost.Geometry (aka GGL, Generic Geometry Library)
Chris@16: 
Chris@16: // Copyright (c) 2007-2012 Barend Gehrels, Amsterdam, the Netherlands.
Chris@16: // Copyright (c) 2008-2012 Bruno Lalande, Paris, France.
Chris@16: // Copyright (c) 2009-2012 Mateusz Loskot, London, UK.
Chris@16: 
Chris@16: // Parts of Boost.Geometry are redesigned from Geodan's Geographic Library
Chris@16: // (geolib/GGL), copyright (c) 1995-2010 Geodan, Amsterdam, the Netherlands.
Chris@16: 
Chris@16: // Use, modification and distribution is subject to the Boost Software License,
Chris@16: // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
Chris@16: // http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: #ifndef BOOST_GEOMETRY_STRATEGIES_CARTESIAN_AREA_SURVEYOR_HPP
Chris@16: #define BOOST_GEOMETRY_STRATEGIES_CARTESIAN_AREA_SURVEYOR_HPP
Chris@16: 
Chris@16: 
Chris@16: #include <boost/mpl/if.hpp>
Chris@16: 
Chris@16: #include <boost/geometry/arithmetic/determinant.hpp>
Chris@16: #include <boost/geometry/core/coordinate_type.hpp>
Chris@16: #include <boost/geometry/core/coordinate_dimension.hpp>
Chris@16: #include <boost/geometry/util/select_most_precise.hpp>
Chris@16: 
Chris@16: 
Chris@16: namespace boost { namespace geometry
Chris@16: {
Chris@16: 
Chris@16: namespace strategy { namespace area
Chris@16: {
Chris@16: 
Chris@16: /*!
Chris@16: \brief Area calculation for cartesian points
Chris@16: \ingroup strategies
Chris@16: \details Calculates area using the Surveyor's formula, a well-known
Chris@16:     triangulation algorithm
Chris@16: \tparam PointOfSegment \tparam_segment_point
Chris@16: \tparam CalculationType \tparam_calculation
Chris@16: 
Chris@16: \qbk{
Chris@16: [heading See also]
Chris@16: [link geometry.reference.algorithms.area.area_2_with_strategy area (with strategy)]
Chris@16: }
Chris@16: 
Chris@16: */
Chris@16: template
Chris@16: <
Chris@16:     typename PointOfSegment,
Chris@16:     typename CalculationType = void
Chris@16: >
Chris@16: class surveyor
Chris@16: {
Chris@16: public :
Chris@16:     // If user specified a calculation type, use that type,
Chris@16:     //   whatever it is and whatever the point-type is.
Chris@16:     // Else, use the pointtype, but at least double
Chris@16:     typedef typename
Chris@16:         boost::mpl::if_c
Chris@16:         <
Chris@16:             boost::is_void<CalculationType>::type::value,
Chris@16:             typename select_most_precise
Chris@16:             <
Chris@16:                 typename coordinate_type<PointOfSegment>::type,
Chris@16:                 double
Chris@16:             >::type,
Chris@16:             CalculationType
Chris@16:         >::type return_type;
Chris@16: 
Chris@16: 
Chris@16: private :
Chris@16: 
Chris@16:     class summation
Chris@16:     {
Chris@16:         friend class surveyor;
Chris@16: 
Chris@16:         return_type sum;
Chris@16:     public :
Chris@16: 
Chris@16:         inline summation() : sum(return_type())
Chris@16:         {
Chris@16:             // Strategy supports only 2D areas
Chris@16:             assert_dimension<PointOfSegment, 2>();
Chris@16:         }
Chris@16:         inline return_type area() const
Chris@16:         {
Chris@16:             return_type result = sum;
Chris@16:             return_type const two = 2;
Chris@16:             result /= two;
Chris@16:             return result;
Chris@16:         }
Chris@16:     };
Chris@16: 
Chris@16: public :
Chris@16:     typedef summation state_type;
Chris@16:     typedef PointOfSegment segment_point_type;
Chris@16: 
Chris@16:     static inline void apply(PointOfSegment const& p1,
Chris@16:                 PointOfSegment const& p2,
Chris@16:                 summation& state)
Chris@16:     {
Chris@16:         // SUM += x2 * y1 - x1 * y2;
Chris@16:         state.sum += detail::determinant<return_type>(p2, p1);
Chris@16:     }
Chris@16: 
Chris@16:     static inline return_type result(summation const& state)
Chris@16:     {
Chris@16:         return state.area();
Chris@16:     }
Chris@16: 
Chris@16: };
Chris@16: 
Chris@16: #ifndef DOXYGEN_NO_STRATEGY_SPECIALIZATIONS
Chris@16: 
Chris@16: namespace services
Chris@16: {
Chris@16:     template <typename Point>
Chris@16:     struct default_strategy<cartesian_tag, Point>
Chris@16:     {
Chris@16:         typedef strategy::area::surveyor<Point> type;
Chris@16:     };
Chris@16: 
Chris@16: } // namespace services
Chris@16: 
Chris@16: #endif // DOXYGEN_NO_STRATEGY_SPECIALIZATIONS
Chris@16: 
Chris@16: 
Chris@16: }} // namespace strategy::area
Chris@16: 
Chris@16: 
Chris@16: 
Chris@16: }} // namespace boost::geometry
Chris@16: 
Chris@16: 
Chris@16: #endif // BOOST_GEOMETRY_STRATEGIES_CARTESIAN_AREA_SURVEYOR_HPP