// Boost.Geometry (aka GGL, Generic Geometry Library)
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// Copyright (c) 2019 Barend Gehrels, 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_ALGORITHMS_DETAIL_OVERLAY_GET_DISTANCE_MEASURE_HPP
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#define BOOST_GEOMETRY_ALGORITHMS_DETAIL_OVERLAY_GET_DISTANCE_MEASURE_HPP
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#include <boost/geometry/core/access.hpp>
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#include <boost/geometry/core/coordinate_system.hpp>
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#include <boost/geometry/core/coordinate_type.hpp>
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#include <boost/geometry/arithmetic/infinite_line_functions.hpp>
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#include <boost/geometry/algorithms/detail/make/make.hpp>
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#include <boost/geometry/algorithms/not_implemented.hpp>
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#include <boost/geometry/util/select_coordinate_type.hpp>
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#include <cmath>
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namespace boost { namespace geometry
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{
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#ifndef DOXYGEN_NO_DETAIL
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namespace detail
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{
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template <typename T>
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struct distance_measure
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{
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T measure;
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distance_measure()
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: measure(T())
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{}
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// Returns true if the distance measure is small.
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// This is an arbitrary boundary, to enable some behaviour
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// (for example include or exclude turns), which are checked later
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// with other conditions.
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bool is_small() const { return geometry::math::abs(measure) < 1.0e-3; }
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// Returns true if the distance measure is absolutely zero
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bool is_zero() const
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{
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return ! is_positive() && ! is_negative();
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}
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// Returns true if the distance measure is positive. Distance measure
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// algorithm returns positive value if it is located on the left side.
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bool is_positive() const { return measure > T(0); }
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// Returns true if the distance measure is negative. Distance measure
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// algorithm returns negative value if it is located on the right side.
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bool is_negative() const { return measure < T(0); }
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};
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} // detail
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namespace detail_dispatch
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{
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// TODO: this is effectively a strategy, but for internal usage.
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// It might be moved to the strategies folder.
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template <typename CalculationType, typename CsTag>
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struct get_distance_measure
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: not_implemented<CsTag>
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{};
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template <typename CalculationType>
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struct get_distance_measure<CalculationType, cartesian_tag>
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{
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typedef detail::distance_measure<CalculationType> result_type;
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template <typename SegmentPoint, typename Point>
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static result_type apply(SegmentPoint const& p1, SegmentPoint const& p2,
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Point const& p)
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{
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// Get the distance measure / side value
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// It is not a real distance and purpose is
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// to detect small differences in collinearity
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typedef model::infinite_line<CalculationType> line_type;
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line_type const line = detail::make::make_infinite_line<CalculationType>(p1, p2);
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result_type result;
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result.measure = arithmetic::side_value(line, p);
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return result;
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}
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};
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template <typename CalculationType>
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struct get_distance_measure<CalculationType, spherical_tag>
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{
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typedef detail::distance_measure<CalculationType> result_type;
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template <typename SegmentPoint, typename Point>
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static result_type apply(SegmentPoint const& , SegmentPoint const& ,
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Point const& )
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{
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// TODO, optional
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result_type result;
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return result;
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}
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};
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template <typename CalculationType>
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struct get_distance_measure<CalculationType, geographic_tag>
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: get_distance_measure<CalculationType, spherical_tag> {};
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} // namespace detail_dispatch
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namespace detail
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{
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// Returns a (often very tiny) value to indicate its side, and distance,
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// 0 (absolutely 0, not even an epsilon) means collinear. Like side,
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// a negative means that p is to the right of p1-p2. And a positive value
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// means that p is to the left of p1-p2.
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template <typename SegmentPoint, typename Point>
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static distance_measure<typename select_coordinate_type<SegmentPoint, Point>::type>
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get_distance_measure(SegmentPoint const& p1, SegmentPoint const& p2, Point const& p)
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{
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typedef typename geometry::cs_tag<Point>::type cs_tag;
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return detail_dispatch::get_distance_measure
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<
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typename select_coordinate_type<SegmentPoint, Point>::type,
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cs_tag
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>::apply(p1, p2, p);
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}
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} // namespace detail
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#endif // DOXYGEN_NO_DETAIL
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}} // namespace boost::geometry
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#endif // BOOST_GEOMETRY_ALGORITHMS_DETAIL_OVERLAY_GET_DISTANCE_MEASURE_HPP
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