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// Boost.Geometry (aka GGL, Generic Geometry Library)
// Copyright (c) 2007-2012 Barend Gehrels, Amsterdam, the Netherlands.
// Copyright (c) 2008-2012 Bruno Lalande, Paris, France.
// Copyright (c) 2009-2012 Mateusz Loskot, London, UK.
// This file was modified by Oracle on 2016, 2017.
// Modifications copyright (c) 2016-2017, Oracle and/or its affiliates.
// 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_STRATEGIES_CARTESIAN_AREA_SURVEYOR_HPP
#define BOOST_GEOMETRY_STRATEGIES_CARTESIAN_AREA_SURVEYOR_HPP
#include <boost/mpl/if.hpp>
//#include <boost/geometry/arithmetic/determinant.hpp>
#include <boost/geometry/core/coordinate_type.hpp>
#include <boost/geometry/core/coordinate_dimension.hpp>
#include <boost/geometry/strategies/area.hpp>
#include <boost/geometry/util/select_most_precise.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;
return_type const two = 2;
result /= two;
return result;
}
};
public :
typedef summation state_type;
typedef PointOfSegment segment_point_type;
static inline void apply(PointOfSegment const& p1,
PointOfSegment const& p2,
summation& state)
{
// Below formulas are equivalent, however the two lower ones
// suffer less from accuracy loss for great values of coordinates.
// See: https://svn.boost.org/trac/boost/ticket/11928
// SUM += x2 * y1 - x1 * y2;
// state.sum += detail::determinant<return_type>(p2, p1);
// SUM += (x2 - x1) * (y2 + y1)
//state.sum += (return_type(get<0>(p2)) - return_type(get<0>(p1)))
// * (return_type(get<1>(p2)) + return_type(get<1>(p1)));
// SUM += (x1 + x2) * (y1 - y2)
state.sum += (return_type(get<0>(p1)) + return_type(get<0>(p2)))
* (return_type(get<1>(p1)) - return_type(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
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