Provide easier way to recognize contours in the mesh (#28)

src/Triangle/Geometry/IPolygon.cs

@@ -69,6 +69,13 @@ namespace TriangleNet.Geometry
         /// <param name="index">The index of the segment endpoint to add to the points list (must be 0 or 1).</param>
         void Add(ISegment segment, int index);
 
+        /// <summary>
+        /// Add a contour to the polygon.
+        /// </summary>
+        /// <param name="contour">The contour to insert.</param>
+        /// <param name="regionlabel">label to ease finding contours in the created mesh.</param>
+        void Add(Contour contour, int regionlabel );
+
         /// <summary>
         /// Add a contour to the polygon.
         /// </summary>

src/Triangle/Geometry/Polygon.cs

@@ -111,6 +111,23 @@ namespace TriangleNet.Geometry
             points.Add(segment.GetVertex(index));
         }
 
+        private void AddContourPointsAndSegments(Contour contour)
+        {
+            points.AddRange(contour.Points);
+            segments.AddRange(contour.GetSegments());
+        }
+
+        /// <inheritdoc />
+        public void Add(Contour contour, int regionlabel )
+        {
+            if (regionlabel != 0)
+            {
+                var interiorPoint = contour.FindInteriorPoint();
+                Regions.Add(new RegionPointer(interiorPoint.X, interiorPoint.Y, regionlabel));
+            }
+            AddContourPointsAndSegments(contour);
+        }
+
         /// <inheritdoc />
         public void Add(Contour contour, bool hole = false)
         {
@@ -120,17 +137,14 @@ namespace TriangleNet.Geometry
             }
             else
             {
-                points.AddRange(contour.Points);
-                segments.AddRange(contour.GetSegments());
+                AddContourPointsAndSegments(contour);
             }
         }
 
         /// <inheritdoc />
         public void Add(Contour contour, Point hole)
         {
-            points.AddRange(contour.Points);
-            segments.AddRange(contour.GetSegments());
-
+            AddContourPointsAndSegments(contour);
             holes.Add(hole);
         }
     }