fixed dissolve linestring->ring

[SVN r61039]

include/boost/geometry/algorithms/dissolve.hpp

@@ -145,6 +145,10 @@ struct dissolve<ring_tag, ring_tag, Ring, RingOut>
         (e.g. vector of "intersection/turn point"'s)
     \param geometry first geometry
     \param output container which will contain dissolved geometry
+    \note Currently dissolve with a (multi)linestring does NOT remove internal
+        overlap, it only tries to connect multiple line end-points.
+        TODO: we should change this behaviour and add a separate "connect" 
+        algorithm, and let dissolve work like polygon.
  */
 template
 <

include/boost/geometry/multi/algorithms/dissolve.hpp

@@ -108,19 +108,27 @@ struct dissolve_multi_linestring
     }
 
     static inline map_iterator_type find_start(map_type const& map,
-            std::map<int, bool>& included)
+            std::map<int, bool>& included, int expected_count = 1)
     {
         for (map_iterator_type it = map.begin();
             it != map.end();
             ++it)
         {
             int count = map.count(it->first);
-            if (count == 1 && ! included[it->second.index])
+            if (count == expected_count && ! included[it->second.index])
             {
                 included[it->second.index] = true;
                 return it;
             }
         }
+
+        // Not found with one point, try one with two points
+        // to find rings
+        if (expected_count == 1)
+        {
+            return find_start(map, included, 2);
+        }
+
         return map.end();
     }
 

test/multi/algorithms/multi_dissolve.cpp

@@ -78,6 +78,12 @@ void test_all()
     test_one<multi_linestring, linestring>("ls_simplex_two",
         "MULTILINESTRING((0 0,1 1),(1 1,2 2),(3 3,4 4),(4 4,5 5))",
         0, 6, 4 * std::sqrt(2.0));
+
+    // Linestrings forming a ring
+    test_one<multi_linestring, linestring>("ls_simplex_ring",
+        "MULTILINESTRING((0 0,0 1),(1 1,1 0),(0 1,1 1),(1 0,0 0))",
+        0, 5, 4.0);
+
 }