132 lines
3.1 KiB
C++
132 lines
3.1 KiB
C++
// Boost.Geometry (aka GGL, Generic Geometry Library)
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// Copyright (c) 2007-2011 Barend Gehrels, Amsterdam, the Netherlands.
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// Copyright (c) 2008-2011 Bruno Lalande, Paris, France.
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// Copyright (c) 2009-2011 Mateusz Loskot, London, UK.
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// Parts of Boost.Geometry are redesigned from Geodan's Geographic Library
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// (geolib/GGL), copyright (c) 1995-2010 Geodan, Amsterdam, the Netherlands.
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// Use, modification and distribution is subject to the Boost Software License,
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// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_GEOMETRY_STRATEGIES_CARTESIAN_AREA_SURVEYOR_HPP
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#define BOOST_GEOMETRY_STRATEGIES_CARTESIAN_AREA_SURVEYOR_HPP
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#include <boost/mpl/if.hpp>
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#include <boost/type_traits.hpp>
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#include <boost/geometry/geometries/point_xy.hpp>
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namespace boost { namespace geometry
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{
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namespace strategy { namespace area
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{
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/*!
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\brief Area calculation for cartesian points
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\ingroup strategies
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\details Calculates area using the Surveyor's formula, a well-known
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triangulation algorithm
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\tparam PointOfSegment \tparam_segment_point
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\tparam CalculationType \tparam_calculation
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\qbk{
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[heading See also]
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[link geometry.reference.algorithms.area.area_2_with_strategy area (with strategy)]
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}
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*/
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template
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<
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typename PointOfSegment,
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typename CalculationType = void
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>
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class surveyor
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{
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public :
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// If user specified a calculation type, use that type,
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// whatever it is and whatever the point-type is.
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// Else, use the pointtype, but at least double
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typedef typename
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boost::mpl::if_c
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<
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boost::is_void<CalculationType>::type::value,
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typename select_most_precise
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<
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typename coordinate_type<PointOfSegment>::type,
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double
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>::type,
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CalculationType
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>::type return_type;
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private :
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class summation
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{
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friend class surveyor;
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return_type sum;
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public :
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inline summation() : sum(return_type())
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{
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// Strategy supports only 2D areas
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assert_dimension<PointOfSegment, 2>();
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}
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inline return_type area() const
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{
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return_type result = sum;
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result /= 2;
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return result;
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}
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};
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public :
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typedef summation state_type;
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typedef PointOfSegment segment_point_type;
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static inline void apply(PointOfSegment const& p1,
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PointOfSegment const& p2,
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summation& state)
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{
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// SUM += x2 * y1 - x1 * y2;
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state.sum += get<0>(p2) * get<1>(p1) - get<0>(p1) * get<1>(p2);
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}
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static inline return_type result(summation const& state)
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{
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return state.area();
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}
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};
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#ifndef DOXYGEN_NO_STRATEGY_SPECIALIZATIONS
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namespace services
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{
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template <typename Point>
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struct default_strategy<cartesian_tag, Point>
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{
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typedef strategy::area::surveyor<Point> type;
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};
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} // namespace services
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#endif // DOXYGEN_NO_STRATEGY_SPECIALIZATIONS
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}} // namespace strategy::area
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}} // namespace boost::geometry
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#endif // BOOST_GEOMETRY_STRATEGIES_CARTESIAN_AREA_SURVEYOR_HPP
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