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authorDongHun Kwak <dh0128.kwak@samsung.com>2016-03-21 06:45:20 (GMT)
committerDongHun Kwak <dh0128.kwak@samsung.com>2016-03-21 06:46:37 (GMT)
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Change-Id: If0072143aa26874812e0db6872e1efb10a3e5e94 Signed-off-by: DongHun Kwak <dh0128.kwak@samsung.com>
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+// Boost.Geometry (aka GGL, Generic Geometry Library)
+
+// Copyright (c) 2015 Barend Gehrels, 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_SIDE_OF_INTERSECTION_HPP
+#define BOOST_GEOMETRY_STRATEGIES_CARTESIAN_SIDE_OF_INTERSECTION_HPP
+
+
+#include <boost/geometry/arithmetic/determinant.hpp>
+#include <boost/geometry/core/access.hpp>
+#include <boost/geometry/core/coordinate_type.hpp>
+#include <boost/geometry/util/math.hpp>
+
+
+namespace boost { namespace geometry
+{
+
+namespace strategy { namespace side
+{
+
+// Calculates the side of the intersection-point (if any) of
+// of segment a//b w.r.t. segment c
+// This is calculated without (re)calculating the IP itself again and fully
+// based on integer mathematics; there are no divisions
+// It can be used for either integer (rescaled) points, and also for FP
+class side_of_intersection
+{
+public :
+
+ // Calculates the side of the intersection-point (if any) of
+ // of segment a//b w.r.t. segment c
+ // This is calculated without (re)calculating the IP itself again and fully
+ // based on integer mathematics
+ template <typename T, typename Segment>
+ static inline T side_value(Segment const& a, Segment const& b,
+ Segment const& c)
+ {
+ // The first point of the three segments is reused several times
+ T const ax = get<0, 0>(a);
+ T const ay = get<0, 1>(a);
+ T const bx = get<0, 0>(b);
+ T const by = get<0, 1>(b);
+ T const cx = get<0, 0>(c);
+ T const cy = get<0, 1>(c);
+
+ T const dx_a = get<1, 0>(a) - ax;
+ T const dy_a = get<1, 1>(a) - ay;
+
+ T const dx_b = get<1, 0>(b) - bx;
+ T const dy_b = get<1, 1>(b) - by;
+
+ T const dx_c = get<1, 0>(c) - cx;
+ T const dy_c = get<1, 1>(c) - cy;
+
+ // Cramer's rule: d (see cart_intersect.hpp)
+ T const d = geometry::detail::determinant<T>
+ (
+ dx_a, dy_a,
+ dx_b, dy_b
+ );
+
+ T const zero = T();
+ if (d == zero)
+ {
+ // There is no IP of a//b, they are collinear or parallel
+ // We don't have to divide but we can already conclude the side-value
+ // is meaningless and the resulting determinant will be 0
+ return zero;
+ }
+
+ // Cramer's rule: da (see cart_intersect.hpp)
+ T const da = geometry::detail::determinant<T>
+ (
+ dx_b, dy_b,
+ ax - bx, ay - by
+ );
+
+ // IP is at (ax + (da/d) * dx_a, ay + (da/d) * dy_a)
+ // Side of IP is w.r.t. c is: determinant(dx_c, dy_c, ipx-cx, ipy-cy)
+ // We replace ipx by expression above and multiply each term by d
+ T const result = geometry::detail::determinant<T>
+ (
+ dx_c * d, dy_c * d,
+ d * (ax - cx) + dx_a * da, d * (ay - cy) + dy_a * da
+ );
+
+ // Note: result / (d * d)
+ // is identical to the side_value of side_by_triangle
+ // Therefore, the sign is always the same as that result, and the
+ // resulting side (left,right,collinear) is the same
+
+ return result;
+
+ }
+
+ template <typename Segment>
+ static inline int apply(Segment const& a, Segment const& b, Segment const& c)
+ {
+ typedef typename geometry::coordinate_type<Segment>::type coordinate_type;
+ coordinate_type const s = side_value<coordinate_type>(a, b, c);
+ coordinate_type const zero = coordinate_type();
+ return math::equals(s, zero) ? 0
+ : s > zero ? 1
+ : -1;
+ }
+
+};
+
+
+}} // namespace strategy::side
+
+}} // namespace boost::geometry
+
+
+#endif // BOOST_GEOMETRY_STRATEGIES_CARTESIAN_SIDE_OF_INTERSECTION_HPP