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// Boost.Geometry (aka GGL, Generic Geometry Library)
// Copyright (c) 2016-2017 Oracle and/or its affiliates.
// Contributed and/or modified by Vissarion Fisikopoulos, on behalf of Oracle
// Contributed and/or modified by Adam Wulkiewicz, on behalf of Oracle
// 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_SPHERICAL_AREA_HPP
#define BOOST_GEOMETRY_STRATEGIES_SPHERICAL_AREA_HPP
#include <boost/geometry/formulas/area_formulas.hpp>
#include <boost/geometry/core/radius.hpp>
#include <boost/geometry/core/srs.hpp>
#include <boost/geometry/strategies/area.hpp>
namespace boost { namespace geometry
{
namespace strategy { namespace area
{
/*!
\brief Spherical area calculation
\ingroup strategies
\details Calculates area on the surface of a sphere using the trapezoidal rule
\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 spherical
{
// Enables special handling of long segments
static const bool LongSegment = false;
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 CT;
protected :
struct excess_sum
{
CT m_sum;
// Keep track if encircles some pole
size_t m_crosses_prime_meridian;
inline excess_sum()
: m_sum(0)
, m_crosses_prime_meridian(0)
{}
template <typename SphereType>
inline CT area(SphereType sphere) const
{
CT result;
CT radius = geometry::get_radius<0>(sphere);
// Encircles pole
if(m_crosses_prime_meridian % 2 == 1)
{
size_t times_crosses_prime_meridian
= 1 + (m_crosses_prime_meridian / 2);
result = CT(2)
* geometry::math::pi<CT>()
* times_crosses_prime_meridian
- geometry::math::abs(m_sum);
if(geometry::math::sign<CT>(m_sum) == 1)
{
result = - result;
}
} else {
result = m_sum;
}
result *= radius * radius;
return result;
}
};
public :
typedef CT return_type;
typedef PointOfSegment segment_point_type;
typedef excess_sum state_type;
typedef geometry::srs::sphere<CT> sphere_type;
// For backward compatibility reasons the radius is set to 1
inline spherical()
: m_sphere(1.0)
{}
template <typename T>
explicit inline spherical(geometry::srs::sphere<T> const& sphere)
: m_sphere(geometry::get_radius<0>(sphere))
{}
explicit inline spherical(CT const& radius)
: m_sphere(radius)
{}
inline void apply(PointOfSegment const& p1,
PointOfSegment const& p2,
excess_sum& state) const
{
if (! geometry::math::equals(get<0>(p1), get<0>(p2)))
{
state.m_sum += geometry::formula::area_formulas
<CT>::template spherical<LongSegment>(p1, p2);
// Keep track whenever a segment crosses the prime meridian
geometry::formula::area_formulas
<CT>::crosses_prime_meridian(p1, p2, state);
}
}
inline return_type result(excess_sum const& state) const
{
return state.area(m_sphere);
}
private :
/// srs Sphere
sphere_type m_sphere;
};
#ifndef DOXYGEN_NO_STRATEGY_SPECIALIZATIONS
namespace services
{
template <typename Point>
struct default_strategy<spherical_equatorial_tag, Point>
{
typedef strategy::area::spherical<Point> type;
};
// Note: spherical polar coordinate system requires "get_as_radian_equatorial"
template <typename Point>
struct default_strategy<spherical_polar_tag, Point>
{
typedef strategy::area::spherical<Point> type;
};
} // namespace services
#endif // DOXYGEN_NO_STRATEGY_SPECIALIZATIONS
}} // namespace strategy::area
}} // namespace boost::geometry
#endif // BOOST_GEOMETRY_STRATEGIES_SPHERICAL_AREA_HPP
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