From 085d641dabebe3fde9839f3a07368aefcc9a98d7 Mon Sep 17 00:00:00 2001
From: Barend Gehrels <barend@xs4all.nl>
Date: Sat, 31 Oct 2015 20:06:39 +0100
Subject: [PATCH] [difference] fix colocations

---
 .../detail/overlay/enrich_intersection_points.hpp    |  8 +++++++-
 .../algorithms/detail/overlay/handle_colocations.hpp | 12 +++++++++++-
 .../set_operations/difference/difference.cpp         |  8 ++++++--
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/include/boost/geometry/algorithms/detail/overlay/enrich_intersection_points.hpp b/include/boost/geometry/algorithms/detail/overlay/enrich_intersection_points.hpp
index ef11038e7..bc8428624 100644
--- a/include/boost/geometry/algorithms/detail/overlay/enrich_intersection_points.hpp
+++ b/include/boost/geometry/algorithms/detail/overlay/enrich_intersection_points.hpp
@@ -515,6 +515,12 @@ inline void enrich_intersection_points(TurnPoints& turn_points,
         {
             check_colocations = true;
         }
+        else if (OverlayType == overlay_difference
+                 && it->both(detail::overlay::operation_intersection))
+        {
+            // For difference operation (u/u -> i/i)
+            check_colocations = true;
+        }
         else if (it->both(detail::overlay::operation_none))
         {
             it->discarded = true;
@@ -523,7 +529,7 @@ inline void enrich_intersection_points(TurnPoints& turn_points,
 
     if (check_colocations)
     {
-        detail::overlay::handle_colocations(turn_points);
+        detail::overlay::handle_colocations<OverlayType>(turn_points);
     }
 
     // Create a map of vectors of indexed operation-types to be able
diff --git a/include/boost/geometry/algorithms/detail/overlay/handle_colocations.hpp b/include/boost/geometry/algorithms/detail/overlay/handle_colocations.hpp
index 336f35572..6457971d2 100644
--- a/include/boost/geometry/algorithms/detail/overlay/handle_colocations.hpp
+++ b/include/boost/geometry/algorithms/detail/overlay/handle_colocations.hpp
@@ -15,6 +15,7 @@
 #include <vector>
 
 #include <boost/range.hpp>
+#include <boost/geometry/algorithms/detail/overlay/overlay_type.hpp>
 #include <boost/geometry/algorithms/detail/overlay/turn_info.hpp>
 #include <boost/geometry/algorithms/detail/ring_identifier.hpp>
 #include <boost/geometry/algorithms/detail/overlay/segment_identifier.hpp>
@@ -96,7 +97,7 @@ private:
 // This function can be extended to replace handle_tangencies: at each
 // colocation incoming and outgoing vectors should be inspected
 
-template <typename TurnPoints>
+template <overlay_type OverlayType, typename TurnPoints>
 inline void handle_colocations(TurnPoints& turn_points)
 {
     typedef typename boost::range_value<TurnPoints>::type turn_type;
@@ -210,6 +211,15 @@ inline void handle_colocations(TurnPoints& turn_points)
                         turn.discarded = true;
                         turn.colocated = true;
                     }
+                    else if (OverlayType == overlay_difference
+                             && turn.both(operation_intersection)
+                             && colocated_ext_int)
+                    {
+                        // For difference (polygon inside out) we need to
+                        // discard i/i instead, in case of colocations
+                        turn.discarded = true;
+                        turn.colocated = true;
+                    }
                 }
                 else
                 {
diff --git a/test/algorithms/set_operations/difference/difference.cpp b/test/algorithms/set_operations/difference/difference.cpp
index 1cb69650f..4894a2a8a 100644
--- a/test/algorithms/set_operations/difference/difference.cpp
+++ b/test/algorithms/set_operations/difference/difference.cpp
@@ -677,16 +677,20 @@ void test_all()
     ***/
 
 #ifdef BOOST_GEOMETRY_TEST_ENABLE_FAILING
+
     test_one<polygon, polygon, polygon>("ticket_11725_2",
         ticket_11725_2[0], ticket_11725_2[1],
         2, -1, 7.5, 0, -1, 0.0);
     test_one<polygon, polygon, polygon>("mysql_21977775",
         mysql_21977775[0], mysql_21977775[1],
         2, -1, 160.856568913, 2, -1, 92.3565689126);
+#endif
+
     test_one<polygon, polygon, polygon>("mysql_21965285",
         mysql_21965285[0], mysql_21965285[1],
-        1, -1, 92.0, 0, -1, 0.0);
-#endif
+        1, -1, 92.0,
+        1, -1, 14.0,
+        1, -1, 92.0 + 14.0);
 }
 
 /*******