| // Boost.Geometry (aka GGL, Generic Geometry Library) |
| |
| // Copyright (c) 2007-2011 Barend Gehrels, Amsterdam, the Netherlands. |
| // Copyright (c) 2008-2011 Bruno Lalande, Paris, France. |
| // Copyright (c) 2009-2011 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_STRATEGIES_CARTESIAN_AREA_SURVEYOR_HPP |
| #define BOOST_GEOMETRY_STRATEGIES_CARTESIAN_AREA_SURVEYOR_HPP |
| |
| |
| #include <boost/mpl/if.hpp> |
| #include <boost/type_traits.hpp> |
| |
| #include <boost/geometry/geometries/point_xy.hpp> |
| |
| |
| namespace boost { namespace geometry |
| { |
| |
| namespace strategy { namespace area |
| { |
| |
| /*! |
| \brief Area calculation for cartesian points |
| \ingroup strategies |
| \details Calculates area using the Surveyor's formula, a well-known |
| triangulation algorithm |
| \tparam PointOfSegment \tparam_segment_point |
| \tparam CalculationType \tparam_calculation |
| |
| \qbk{ |
| [heading See also] |
| [link geometry.reference.algorithms.area.area_2_with_strategy area (with strategy)] |
| } |
| |
| */ |
| template |
| < |
| typename PointOfSegment, |
| typename CalculationType = void |
| > |
| class surveyor |
| { |
| public : |
| // If user specified a calculation type, use that type, |
| // whatever it is and whatever the point-type is. |
| // Else, use the pointtype, but at least double |
| typedef typename |
| boost::mpl::if_c |
| < |
| boost::is_void<CalculationType>::type::value, |
| typename select_most_precise |
| < |
| typename coordinate_type<PointOfSegment>::type, |
| double |
| >::type, |
| CalculationType |
| >::type return_type; |
| |
| |
| private : |
| |
| class summation |
| { |
| friend class surveyor; |
| |
| return_type sum; |
| public : |
| |
| inline summation() : sum(return_type()) |
| { |
| // Strategy supports only 2D areas |
| assert_dimension<PointOfSegment, 2>(); |
| } |
| inline return_type area() const |
| { |
| return_type result = sum; |
| result *= 0.5; |
| return result; |
| } |
| }; |
| |
| public : |
| typedef summation state_type; |
| typedef PointOfSegment segment_point_type; |
| |
| static inline void apply(PointOfSegment const& p1, |
| PointOfSegment const& p2, |
| summation& state) |
| { |
| // SUM += x2 * y1 - x1 * y2; |
| state.sum += get<0>(p2) * get<1>(p1) - get<0>(p1) * get<1>(p2); |
| } |
| |
| static inline return_type result(summation const& state) |
| { |
| return state.area(); |
| } |
| |
| }; |
| |
| #ifndef DOXYGEN_NO_STRATEGY_SPECIALIZATIONS |
| |
| namespace services |
| { |
| template <typename Point> |
| struct default_strategy<cartesian_tag, Point> |
| { |
| typedef strategy::area::surveyor<Point> type; |
| }; |
| |
| } // namespace services |
| |
| #endif // DOXYGEN_NO_STRATEGY_SPECIALIZATIONS |
| |
| |
| }} // namespace strategy::area |
| |
| |
| |
| }} // namespace boost::geometry |
| |
| |
| #endif // BOOST_GEOMETRY_STRATEGIES_CARTESIAN_AREA_SURVEYOR_HPP |