From e35a3b1610d61c184bbf810f8d73449d92870957 Mon Sep 17 00:00:00 2001
From: Barend Gehrels <barend@xs4all.nl>
Date: Sat, 11 Feb 2012 14:24:42 +0000
Subject: [PATCH] Boost.Geometry line/poly overlay (new for 1.49), bugfix (take
 point-in-between instead of first point)

[SVN r76975]
---
 .../algorithms/detail/overlay/follow.hpp      | 52 ++++++++++++++-----
 .../detail/overlay/intersection_insert.hpp    | 13 ++++-
 2 files changed, 52 insertions(+), 13 deletions(-)

diff --git a/include/boost/geometry/algorithms/detail/overlay/follow.hpp b/include/boost/geometry/algorithms/detail/overlay/follow.hpp
index 274cc47b8..ac8af1c6c 100644
--- a/include/boost/geometry/algorithms/detail/overlay/follow.hpp
+++ b/include/boost/geometry/algorithms/detail/overlay/follow.hpp
@@ -14,11 +14,12 @@
 #include <boost/range.hpp>
 #include <boost/mpl/assert.hpp>
 
+#include <boost/geometry/algorithms/detail/point_on_border.hpp>
 #include <boost/geometry/algorithms/detail/overlay/append_no_duplicates.hpp>
 #include <boost/geometry/algorithms/detail/overlay/copy_segments.hpp>
 #include <boost/geometry/algorithms/detail/overlay/turn_info.hpp>
 
-#include <boost/geometry/algorithms/within.hpp>
+#include <boost/geometry/algorithms/covered_by.hpp>
 
 
 namespace boost { namespace geometry
@@ -43,6 +44,29 @@ static inline bool is_entering(Turn const& /* TODO remove this parameter */, Ope
         ;
 }
 
+template 
+<
+    typename Turn, 
+    typename Operation, 
+    typename LineString, 
+    typename Polygon
+>
+static inline bool last_covered_by(Turn const& turn, Operation const& op, 
+                LineString const& linestring, Polygon const& polygon)
+{
+    // Check any point between the this one and the first IP 
+    typedef typename geometry::point_type<LineString>::type point_type;
+    point_type point_in_between;
+    detail::point_on_border::midpoint_helper
+        <
+            point_type,
+            0, dimension<point_type>::value
+        >::apply(point_in_between, linestring[op.seg_id.segment_index], turn.point);
+
+    return geometry::covered_by(point_in_between, polygon);
+}
+
+
 template 
 <
     typename Turn, 
@@ -58,7 +82,7 @@ static inline bool is_leaving(Turn const& turn, Operation const& op,
     {
         return entered 
             || turn.method == method_crosses
-            || (first && geometry::within(linestring[0], polygon))
+            || (first && last_covered_by(turn, op, linestring, polygon))
             ;
     }
     return false;
@@ -79,27 +103,31 @@ static inline bool is_staying_inside(Turn const& turn, Operation const& op,
     if (turn.method == method_crosses)
     {
         // The normal case, this is completely covered with entering/leaving 
-        // so stay out of this time consuming "within"
+        // so stay out of this time consuming "covered_by"
         return false;
     }
 
     if (is_entering(turn, op))
     {
-        return entered || (first && geometry::within(linestring[0], polygon));
+        return entered || (first && last_covered_by(turn, op, linestring, polygon));
     }
 
     return false;
 }
 
-template <typename Turn>
-static inline bool was_entered(Turn const& turn, bool first)
+template 
+<
+    typename Turn, 
+    typename Operation, 
+    typename Linestring, 
+    typename Polygon
+>
+static inline bool was_entered(Turn const& turn, Operation const& op, bool first,
+                Linestring const& linestring, Polygon const& polygon)
 {
     if (first && (turn.method == method_collinear || turn.method == method_equal))
     {
-        // If it is the very first point, and either equal or collinear, there is only one
-        // IP generated (on purpose). So consider this as having entered. 
-        // Maybe it will leave immediately after that (u/i) but that is checked later.
-        return true;
+        return last_covered_by(turn, op, linestring, polygon);
     }
     return false;
 }
@@ -169,7 +197,7 @@ struct action_selector<overlay_intersection>
     template <typename Point, typename Geometry>
     static inline bool included(Point const& point, Geometry const& geometry)
     {
-        return geometry::within(point, geometry);
+        return geometry::covered_by(point, geometry);
     }
 
 };
@@ -299,7 +327,7 @@ public :
         {
             turn_operation_iterator_type iit = boost::begin(it->operations);
 
-            if (following::was_entered(*it, first))
+            if (following::was_entered(*it, *iit, first, linestring, polygon))
             {
                 debug_traverse(*it, *iit, "-> Was entered");
                 entered = true;
diff --git a/include/boost/geometry/algorithms/detail/overlay/intersection_insert.hpp b/include/boost/geometry/algorithms/detail/overlay/intersection_insert.hpp
index 45324fc79..8bca790d7 100644
--- a/include/boost/geometry/algorithms/detail/overlay/intersection_insert.hpp
+++ b/include/boost/geometry/algorithms/detail/overlay/intersection_insert.hpp
@@ -22,6 +22,7 @@
 #include <boost/geometry/core/reverse_dispatch.hpp>
 #include <boost/geometry/geometries/concepts/check.hpp>
 #include <boost/geometry/algorithms/convert.hpp>
+#include <boost/geometry/algorithms/detail/point_on_border.hpp>
 #include <boost/geometry/algorithms/detail/overlay/clip_linestring.hpp>
 #include <boost/geometry/algorithms/detail/overlay/get_intersection_points.hpp>
 #include <boost/geometry/algorithms/detail/overlay/overlay.hpp>
@@ -171,7 +172,17 @@ struct intersection_of_linestring_with_areal
             // No intersection points, it is either completely 
             // inside (interior + borders)
             // or completely outside
-            if (follower::included(*boost::begin(linestring), areal))
+
+            // Use border point (on a segment) to check this
+            // (because turn points might skip some cases)
+            point_type border_point;
+            if (! geometry::point_on_border(border_point, linestring, true))
+            {
+                return out;
+            }
+
+
+            if (follower::included(border_point, areal))
             {
                 LineStringOut copy;
                 geometry::convert(linestring, copy);