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131 lines
3.1 KiB
131 lines
3.1 KiB
// 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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