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+// Boost.Geometry (aka GGL, Generic Geometry Library)
+
+// Copyright (c) 2012-2014 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_BUFFER_HPP
+#define BOOST_GEOMETRY_STRATEGIES_CARTESIAN_BUFFER_HPP
+
+namespace boost { namespace geometry
+{
+
+namespace strategy { namespace buffer
+{
+
+/*
+
+   A Buffer-join strategy gets 4 input points.
+   On the two consecutive segments s1 and s2 (joining at vertex v):
+
+   The lines from parallel at s1, s2 (at buffer-distance) end/start
+   in two points perpendicular to the segments: p1 and p2.
+   These parallel lines interesct in point ip
+
+             (s2)
+              |
+              |
+              ^
+              |
+        (p2)  |(v)
+        *     +----<--- (s1)
+
+        x(ip) *(p1)
+
+
+    So, in clockwise order:
+        v : vertex point
+        p1: perpendicular on left side of segment1<1> (perp1)
+        ip: intersection point
+        p2: perpendicular on left side of segment2<0> (perp2)
+*/
+
+
+
+/*!
+\brief Enumerates options for side of buffer (left/right w.r.t. directed
+    segment)
+\ingroup enum
+\details Around a linestring, a buffer can be defined left or right.
+    Around a polygon, assumed clockwise internally,
+    a buffer is either on the left side (inflates the polygon), or on the
+    right side (deflates the polygon)
+*/
+enum buffer_side_selector { buffer_side_left, buffer_side_right };
+
+/*!
+\brief Enumerates types of pieces (parts of buffer) around geometries
+\ingroup enum
+*/
+enum piece_type
+{
+    buffered_segment,
+    buffered_join,
+    buffered_round_end,
+    buffered_flat_end,
+    buffered_point,
+    buffered_concave   // always on the inside
+};
+
+
+/*!
+\brief Enumerates types of joins
+\ingroup enum
+*/
+enum join_selector
+{
+    join_convex,
+    join_concave,
+    join_continue, // collinear, next segment touches previous segment
+    join_spike     // collinear, with overlap, next segment goes back
+};
+
+
+}} // namespace strategy::buffer
+
+
+}} // namespace boost::geometry
+
+#endif // BOOST_GEOMETRY_STRATEGIES_CARTESIAN_BUFFER_HPP