diff --git a/src/Airports/GenAirports850/airport.cxx b/src/Airports/GenAirports850/airport.cxx
index adf25ec2..3a0ae337 100644
--- a/src/Airports/GenAirports850/airport.cxx
+++ b/src/Airports/GenAirports850/airport.cxx
@@ -285,8 +285,8 @@ void Airport::BuildBtg(const std::string& root, const string_list& elev_src )
     tgcontour_list slivers;
     tgcontour_list line_slivers;
 
-    tgPolygon      apt_base;
-    tgPolygon      apt_clearing;
+    tgpolygon_list apt_base_polys;
+    tgpolygon_list apt_clearing_polys;
 
     // runways
     tgpolygon_list rwy_polys;
@@ -397,7 +397,7 @@ void Airport::BuildBtg(const std::string& root, const string_list& elev_src )
             }
             else
             {
-                runways[i]->BuildBtg( rwy_polys, rwy_lights, slivers, apt_base, apt_clearing, shapefile );
+                runways[i]->BuildBtg( rwy_polys, rwy_lights, slivers, apt_base_polys, apt_clearing_polys, shapefile );
             }
 
             // Now try to merge any slivers we found
@@ -433,7 +433,7 @@ void Airport::BuildBtg(const std::string& root, const string_list& elev_src )
             }
             else
             {
-                helipads[i]->BuildBtg( rwy_polys, rwy_lights, slivers, apt_base, apt_clearing );
+                helipads[i]->BuildBtg( rwy_polys, rwy_lights, slivers, apt_base_polys, apt_clearing_polys );
             }
 
             // Now try to merge any slivers we found
@@ -463,7 +463,7 @@ void Airport::BuildBtg(const std::string& root, const string_list& elev_src )
             }
             else
             {
-                pavements[i]->BuildBtg( pvmt_polys, slivers, apt_base, apt_clearing, shapefile );
+                pavements[i]->BuildBtg( pvmt_polys, slivers, apt_base_polys, apt_clearing_polys, shapefile );
             }
 
             // Now try to merge any slivers we found
@@ -497,7 +497,7 @@ void Airport::BuildBtg(const std::string& root, const string_list& elev_src )
             }
             else
             {
-                taxiways[i]->BuildBtg( pvmt_polys, rwy_lights, slivers, apt_base, apt_clearing, shapefile );
+                taxiways[i]->BuildBtg( pvmt_polys, rwy_lights, slivers, apt_base_polys, apt_clearing_polys, shapefile );
             }
 
             // Now try to merge any slivers we found
@@ -517,15 +517,7 @@ void Airport::BuildBtg(const std::string& root, const string_list& elev_src )
             if ( runways[i]->GetsShoulder() )
             {
                 slivers.clear();
-
-                if (boundary.size())
-                {
-                    runways[i]->BuildShoulder( rwy_polys, slivers );
-                }
-                else
-                {
-                    runways[i]->BuildShoulder( rwy_polys, slivers, apt_base, apt_clearing );
-                }
+                runways[i]->BuildShoulder( rwy_polys, slivers );
 
                 // Now try to merge any slivers we found
                 tgPolygon::MergeSlivers( rwy_polys, slivers );
@@ -545,15 +537,7 @@ void Airport::BuildBtg(const std::string& root, const string_list& elev_src )
             if ( helipads[i]->GetsShoulder() )
             {
                 slivers.clear();
-
-                if (boundary.size())
-                {
-                    helipads[i]->BuildShoulder( rwy_polys, slivers );
-                }
-                else
-                {
-                    helipads[i]->BuildShoulder( rwy_polys, slivers, apt_base, apt_clearing );
-                }
+                helipads[i]->BuildShoulder( rwy_polys, slivers );
 
                 // Now try to merge any slivers we found
                 tgPolygon::MergeSlivers( rwy_polys, slivers );
@@ -563,6 +547,7 @@ void Airport::BuildBtg(const std::string& root, const string_list& elev_src )
     }
 
     // build the base and clearing if there's a boundary
+    tgPolygon apt_base, apt_clearing;
     if (boundary.size())
     {
         SG_LOG(SG_GENERAL, SG_INFO, "Build " << boundary.size() << " Boundary Polys ");
@@ -573,6 +558,9 @@ void Airport::BuildBtg(const std::string& root, const string_list& elev_src )
             SG_LOG(SG_GENERAL, SG_DEBUG, "Build Userdefined boundary " << i + 1 << " of " << boundary.size());
             boundary[i]->BuildBtg( apt_base, apt_clearing, shapefile );
         }
+    } else {
+        apt_base     = tgPolygon::Union( apt_base_polys );
+        apt_clearing = tgPolygon::Union( apt_clearing_polys );
     }
 
     if ( apt_base.TotalNodes() == 0 )
@@ -592,9 +580,6 @@ void Airport::BuildBtg(const std::string& root, const string_list& elev_src )
 
     // add segments to polygons to remove any possible "T"
     // intersections
-    //TGTriNodes tmp_pvmt_nodes;
-    //TGTriNodes tmp_feat_nodes;
-
     UniqueSGGeodSet tmp_pvmt_nodes;
     UniqueSGGeodSet tmp_feat_nodes;
 
@@ -791,7 +776,7 @@ void Airport::BuildBtg(const std::string& root, const string_list& elev_src )
        intersecting contours */
     base_poly = tgPolygon::Simplify( base_poly );
 
-    SG_LOG(SG_GENERAL, SG_INFO, "Tesselating base poly ");
+    SG_LOG(SG_GENERAL, SG_INFO, "Tesselating base poly : " << base_poly.Contours() << " contours " );
     base_poly.Tesselate();
     SG_LOG(SG_GENERAL, SG_INFO, "Tesselating base poly - done : Triangles = " << base_poly.Triangles());
     // should we texture base here?
diff --git a/src/Airports/GenAirports850/closedpoly.cxx b/src/Airports/GenAirports850/closedpoly.cxx
index 5c48c9a3..5c49d49c 100644
--- a/src/Airports/GenAirports850/closedpoly.cxx
+++ b/src/Airports/GenAirports850/closedpoly.cxx
@@ -415,7 +415,7 @@ std::string ClosedPoly::GetMaterial( int surface )
     return material;
 }
 
-int ClosedPoly::BuildBtg( tgpolygon_list& rwy_polys, tgcontour_list& slivers, tgPolygon& apt_base, tgPolygon& apt_clearing, std::string& shapefile_name )
+int ClosedPoly::BuildBtg( tgpolygon_list& rwy_polys, tgcontour_list& slivers, tgpolygon_list& apt_base_polys, tgpolygon_list& apt_clearing_polys, std::string& shapefile_name )
 {
     if (is_pavement && pre_tess.Contours() )
     {
@@ -427,10 +427,10 @@ int ClosedPoly::BuildBtg( tgpolygon_list& rwy_polys, tgcontour_list& slivers, tg
         safe_base = tgPolygon::Expand( pre_tess, 50.0);
 
         // add this to the airport clearing
-        apt_clearing = tgPolygon::Union( safe_base, apt_clearing);
+        apt_clearing_polys.push_back( safe_base );
 
         // and add the clearing to the base
-        apt_base = tgPolygon::Union( base, apt_base );
+        apt_base_polys.push_back( base );
     }
 
     // clean up to save ram : we're done here...
diff --git a/src/Airports/GenAirports850/closedpoly.hxx b/src/Airports/GenAirports850/closedpoly.hxx
index 968895a5..d529beb4 100644
--- a/src/Airports/GenAirports850/closedpoly.hxx
+++ b/src/Airports/GenAirports850/closedpoly.hxx
@@ -30,8 +30,8 @@ public:
 
     int  BuildBtg( tgpolygon_list& rwy_polys,
                    tgcontour_list& slivers,
-                   tgPolygon& apt_base,
-                   tgPolygon& apt_clearing,
+                   tgpolygon_list& apt_base_polys,
+                   tgpolygon_list& apt_clearing_polys,
                    std::string& shapefile_name );
 
     FeatureList* GetFeatures()
@@ -63,11 +63,14 @@ private:
     BezContour* cur_contour;
 
     // outer boundary as convex hull
-    point_list hull;
+    // point_list hull;
 
     // Converted polygon after parsing complete
     tgPolygon pre_tess;
 
+    // shoulders after BTG built
+    tgpolygon_list shoulder_polys;
+
     // pavement definitions have multiple linear features (markings and lights for each contour)
     LinearFeature* cur_feature;
     FeatureList features;
diff --git a/src/Airports/GenAirports850/helipad.cxx b/src/Airports/GenAirports850/helipad.cxx
index 3868c0a4..ff77b103 100644
--- a/src/Airports/GenAirports850/helipad.cxx
+++ b/src/Airports/GenAirports850/helipad.cxx
@@ -200,14 +200,15 @@ void Helipad::BuildBtg( tgpolygon_list& rwy_polys,
 void Helipad::BuildBtg( tgpolygon_list& rwy_polys,
                         tglightcontour_list& rwy_lights,
                         tgcontour_list& slivers,
-                        tgPolygon& apt_base,
-                        tgPolygon& apt_clearing )
+                        tgpolygon_list& apt_base_polys,
+                        tgpolygon_list& apt_clearing_polys )
 {
     BuildBtg( rwy_polys, rwy_lights, slivers );
 
     // generate area around helipad
     double    length, width;
-    tgContour base, safe_base;
+    tgContour base_contour, safe_base_contour;
+    tgPolygon base, safe_base;
 
     length = heli.length;
     width  = heli.width;
@@ -219,45 +220,20 @@ void Helipad::BuildBtg( tgpolygon_list& rwy_polys,
         width += 2.0;
     }
 
-    base      = gen_helipad_area_w_extend(length * 0.25 , width * 0.25 );
-    base      = tgContour::Snap( base, gSnap );
+    base_contour = gen_helipad_area_w_extend(length * 0.25 , width * 0.25 );
+    base_contour = tgContour::Snap( base_contour, gSnap );
+    base.AddContour( base_contour );
 
     // also clear a safe area around the pad
-    safe_base = gen_helipad_area_w_extend( length * 0.5, width * 0.5 );
-    safe_base = tgContour::Snap( safe_base, gSnap );
+    safe_base_contour = gen_helipad_area_w_extend( length * 0.5, width * 0.5 );
+    safe_base_contour = tgContour::Snap( safe_base_contour, gSnap );
+    safe_base.AddContour( safe_base_contour );
 
     // add this to the airport clearing
-    apt_clearing = tgPolygon::Union(safe_base, apt_clearing);
+    apt_clearing_polys.push_back( safe_base );
 
     // and add the clearing to the base
-    apt_base = tgPolygon::Union( base, apt_base );
-}
-
-void Helipad::BuildShoulder( tgpolygon_list& rwy_polys,
-                             tgcontour_list& slivers,
-                             tgPolygon& apt_base,
-                             tgPolygon& apt_clearing )
-{
-    tgPolygon shoulder;
-
-    for (unsigned int i=0; i<shoulder_polys.size(); i++) {
-        shoulder = shoulder_polys[i];
-
-        // Clip the new polygon against what ever has already been created.
-        tgPolygon clipped = tgPolygon::DiffWithAccumulator( shoulder );
-        tgPolygon::RemoveSlivers( clipped, slivers );
-
-        // Split long edges to create an object that can better flow with
-        // the surface terrain
-        tgPolygon split = tgPolygon::SplitLongEdges( clipped, 400.0 );
-        shoulder_polys[i] = split;
-
-        rwy_polys.push_back( shoulder_polys[i] );
-
-        tgPolygon::AddToAccumulator( shoulder );
-    }
-
-    // base and clearing calculated when generating the shoulders
+    apt_base_polys.push_back( base );
 }
 
 void Helipad::BuildShoulder( tgpolygon_list& rwy_polys,
diff --git a/src/Airports/GenAirports850/helipad.hxx b/src/Airports/GenAirports850/helipad.hxx
index 42e65f71..8680dbf0 100644
--- a/src/Airports/GenAirports850/helipad.hxx
+++ b/src/Airports/GenAirports850/helipad.hxx
@@ -30,8 +30,8 @@ public:
     void BuildBtg( tgpolygon_list& heli_polys,
                    tglightcontour_list& heli_lights,
                    tgcontour_list& slivers,
-                   tgPolygon& apt_base,
-                   tgPolygon& apt_clearing );
+                   tgpolygon_list& apt_base_polys,
+                   tgpolygon_list& apt_clearing_polys );
 
     SGGeod GetLoc()
     {
@@ -46,11 +46,6 @@ public:
     void BuildShoulder( tgpolygon_list& rwy_polys,
                         tgcontour_list& slivers );
 
-    void BuildShoulder( tgpolygon_list& rwy_polys,
-                        tgcontour_list& slivers,
-                        tgPolygon& apt_base,
-                        tgPolygon& apt_clearing );
-
 private:
     struct TGRunway {
     // data for helipad
diff --git a/src/Airports/GenAirports850/runway.cxx b/src/Airports/GenAirports850/runway.cxx
index a0b5c5eb..c03c253b 100644
--- a/src/Airports/GenAirports850/runway.cxx
+++ b/src/Airports/GenAirports850/runway.cxx
@@ -166,25 +166,35 @@ int Runway::BuildBtg( tgpolygon_list& rwy_polys, tglightcontour_list& rwy_lights
     return 0;
 }
 
-int Runway::BuildBtg( tgpolygon_list& rwy_polys, tglightcontour_list& rwy_lights, tgcontour_list& slivers, tgPolygon& apt_base, tgPolygon& apt_clearing, std::string& shapefile_name )
+int Runway::BuildBtg( tgpolygon_list& rwy_polys, tglightcontour_list& rwy_lights, tgcontour_list& slivers, tgpolygon_list& apt_base_polys, tgpolygon_list& apt_clearing_polys, std::string& shapefile_name )
 {
-    tgContour base, safe_base;
+    tgContour base_contour, safe_base_contour;
+    tgPolygon base, safe_base;
+    double shoulder_width = 0.0;
 
     BuildBtg( rwy_polys, rwy_lights, slivers, shapefile_name );
 
     // generate area around runways
-    base      = gen_runway_area_w_extend( 20.0, -rwy.overrun[0], -rwy.overrun[1], 20.0 );
-    base      = tgContour::Snap( base, gSnap );
+    if ( (rwy.shoulder > 0) && (rwy.surface < 3) ) {
+        shoulder_width += 22.0;
+    } else if ( (rwy.surface == 1) || (rwy.surface == 2) ) {
+        shoulder_width += 2.0;
+    }
+
+    base_contour      = gen_runway_area_w_extend( 20.0, -rwy.overrun[0], -rwy.overrun[1], shoulder_width + 20.0 );
+    base_contour      = tgContour::Snap( base_contour, gSnap );
+    base.AddContour( base_contour );
 
     // also clear a safe area around the runway
-    safe_base = gen_runway_area_w_extend( 180.0, -rwy.overrun[0], -rwy.overrun[1], 50.0 );
-    safe_base = tgContour::Snap( safe_base, gSnap );
+    safe_base_contour = gen_runway_area_w_extend( 180.0, -rwy.overrun[0], -rwy.overrun[1], shoulder_width + 50.0 );
+    safe_base_contour = tgContour::Snap( safe_base_contour, gSnap );
+    safe_base.AddContour( safe_base_contour );
 
     // add this to the airport clearing
-    apt_clearing = tgPolygon::Union( safe_base, apt_clearing );
+    apt_clearing_polys.push_back( safe_base );
 
     // and add the clearing to the base
-    apt_base = tgPolygon::Union( base, apt_base );
+    apt_base_polys.push_back( base );
 
     return 0;
 }
\ No newline at end of file
diff --git a/src/Airports/GenAirports850/runway.hxx b/src/Airports/GenAirports850/runway.hxx
index 7e9c0022..1f1b90e7 100644
--- a/src/Airports/GenAirports850/runway.hxx
+++ b/src/Airports/GenAirports850/runway.hxx
@@ -39,18 +39,13 @@ public:
     int BuildBtg( tgpolygon_list& rwy_polys,
                   tglightcontour_list& rwy_lights,
                   tgcontour_list& slivers,
-                  tgPolygon& apt_base,
-                  tgPolygon& apt_clearing,
+                  tgpolygon_list& apt_base_polys,
+                  tgpolygon_list& apt_clearing_polys,
                   std::string& shapefile_name );
 
     void BuildShoulder( tgpolygon_list& rwy_polys,
                         tgcontour_list& slivers );
 
-    void BuildShoulder( tgpolygon_list& rwy_polys,
-                        tgcontour_list& slivers,
-                        tgPolygon& apt_base,
-                        tgPolygon& apt_clearing );
-    
 private:
     struct TGRunway {
     // data for whole runway
diff --git a/src/Airports/GenAirports850/rwy_gen.cxx b/src/Airports/GenAirports850/rwy_gen.cxx
index 72ee2f6c..5e5ba171 100644
--- a/src/Airports/GenAirports850/rwy_gen.cxx
+++ b/src/Airports/GenAirports850/rwy_gen.cxx
@@ -847,9 +847,7 @@ void Runway::gen_rwy( tgpolygon_list& rwy_polys,
 }
 
 void Runway::BuildShoulder( tgpolygon_list& rwy_polys,
-                            tgcontour_list& slivers,
-                            tgPolygon& apt_base,
-                            tgPolygon& apt_clearing )
+                            tgcontour_list& slivers )
 {
     tgPolygon base, safe_base;
     tgPolygon shoulder;
@@ -867,40 +865,6 @@ void Runway::BuildShoulder( tgpolygon_list& rwy_polys,
         shoulder_polys[i] = split;
 
         rwy_polys.push_back( shoulder_polys[i] );
-
-        tgPolygon::AddToAccumulator( shoulder );
-
-        // also clear a safe area around the runway
-        base      = tgPolygon::Expand( shoulder, 20.0);
-        safe_base = tgPolygon::Expand( shoulder, 50.0);
-
-        // add this to the airport clearing
-        apt_clearing = tgPolygon::Union( safe_base, apt_clearing );
-
-        // and add the clearing to the base
-        apt_base = tgPolygon::Union( base, apt_base );
-    }
-}
-
-void Runway::BuildShoulder( tgpolygon_list& rwy_polys,
-                            tgcontour_list& slivers )
-{
-    tgPolygon shoulder;
-
-    for (unsigned int i=0; i<shoulder_polys.size(); i++) {
-        shoulder = shoulder_polys[i];
-
-        // Clip the new polygon against what ever has already been created.
-        tgPolygon clipped = tgPolygon::DiffWithAccumulator( shoulder );
-        tgPolygon::RemoveSlivers( clipped, slivers );
-
-        // Split long edges to create an object that can better flow with
-        // the surface terrain
-        tgPolygon split = tgPolygon::SplitLongEdges( clipped, 400.0 );
-        shoulder_polys[i] = split;
-
-        rwy_polys.push_back( shoulder_polys[i] );
-
         tgPolygon::AddToAccumulator( shoulder );
     }
-}
+}
\ No newline at end of file
diff --git a/src/Airports/GenAirports850/taxiway.cxx b/src/Airports/GenAirports850/taxiway.cxx
index 2302c7ac..ab41b2db 100644
--- a/src/Airports/GenAirports850/taxiway.cxx
+++ b/src/Airports/GenAirports850/taxiway.cxx
@@ -159,21 +159,24 @@ int Taxiway::BuildBtg( tgpolygon_list& rwy_polys, tglightcontour_list& rwy_light
     return 0;
 }
 
-int Taxiway::BuildBtg( tgpolygon_list& rwy_polys, tglightcontour_list& rwy_lights, tgcontour_list& slivers, tgPolygon& apt_base, tgPolygon& apt_clearing, std::string& shapefile_name )
+int Taxiway::BuildBtg( tgpolygon_list& rwy_polys, tglightcontour_list& rwy_lights, tgcontour_list& slivers, tgpolygon_list& apt_base_polys, tgpolygon_list& apt_clearing_polys, std::string& shapefile_name )
 {
-    tgContour base, safe_base;
+    tgContour base_contour, safe_base_contour;
+    tgPolygon base, safe_base;
 
     BuildBtg( rwy_polys, rwy_lights, slivers, shapefile_name );
 
-    base = tgContour::Expand( taxi_contour, 20.0);
-
-    safe_base = tgContour::Expand( taxi_contour, 50.0);
+    base_contour = tgContour::Expand( taxi_contour, 20.0);
+    base.AddContour( base_contour );
 
+    safe_base_contour = tgContour::Expand( taxi_contour, 50.0);
+    safe_base.AddContour( safe_base_contour );
+    
     // add this to the airport clearing
-    apt_clearing = tgPolygon::Union( safe_base, apt_clearing);
+    apt_clearing_polys.push_back( safe_base );
 
     // and add the clearing to the base
-    apt_base = tgPolygon::Union( base, apt_base );
+    apt_base_polys.push_back( base );
 
     return 0;
 }
diff --git a/src/Airports/GenAirports850/taxiway.hxx b/src/Airports/GenAirports850/taxiway.hxx
index 3e49c805..2598db07 100644
--- a/src/Airports/GenAirports850/taxiway.hxx
+++ b/src/Airports/GenAirports850/taxiway.hxx
@@ -19,8 +19,8 @@ public:
     int BuildBtg( tgpolygon_list& taxi_polys,
                   tglightcontour_list& taxi_lights,
                   tgcontour_list& slivers,
-                  tgPolygon& apt_base,
-                  tgPolygon& apt_clearing,
+                  tgpolygon_list& apt_base_polys,
+                  tgpolygon_list& apt_clearing_polys,
                   std::string& shapefile_name );
 
 private:
diff --git a/src/BuildTiles/Main/cliptst.cxx b/src/BuildTiles/Main/cliptst.cxx
index 8ebe269f..f2abe26f 100644
--- a/src/BuildTiles/Main/cliptst.cxx
+++ b/src/BuildTiles/Main/cliptst.cxx
@@ -282,7 +282,7 @@ int main(int argc, char* argv[])
   if (argc > 5 && strcasecmp(argv[5], "EVENODD") == 0)
       clip_pft = pftEvenOdd;
 
-  cout << "\nclipping ... ";
+  cout << "\nclipping ... \n";
 
   Clipper c;
   c.AddPolygons(subject, ptSubject);
@@ -302,6 +302,15 @@ int main(int argc, char* argv[])
 //    cout << "\nEllapsed: " << elapsed;
 //  }
 
+  for ( int i=0; i<solution.size(); i++ ) {
+      Polygon contour = solution[i];
+      if ( Orientation( contour ) ) {
+          cout << "solution contour " << i << " is true \n";
+      } else {
+          cout << "solution contour " << i << " is false \n";
+      }
+  }
+
   if (succeeded) {
       SaveToFile("solution.txt", solution, precision);
       SaveToFileOstream("solution_ostream", solution );
diff --git a/src/Lib/Polygon/polygon.cxx b/src/Lib/Polygon/polygon.cxx
index 6873d8df..53cbcdb3 100644
--- a/src/Lib/Polygon/polygon.cxx
+++ b/src/Lib/Polygon/polygon.cxx
@@ -2305,6 +2305,35 @@ tgPolygon tgPolygon::Union( const tgPolygon& subject, tgPolygon& clip )
     return result;
 }
 
+tgPolygon tgPolygon::Union( const tgpolygon_list& polys )
+{
+    ClipperLib::Polygons clipper_result;
+    ClipperLib::Clipper c;
+    TGTriNodes all_nodes;
+    tgPolygon  result;
+
+    /* before union - gather all nodes */
+    for ( unsigned int i=0; i<polys.size(); i++ ) {
+        for ( unsigned int j = 0; j < polys[i].Contours(); ++j ) {
+            for ( unsigned int k = 0; k < polys[i].ContourSize( j ); ++k ) {
+                all_nodes.unique_add( Point3D::fromSGGeod( polys[i].GetNode(j, k) ) );
+            }
+        }
+    }
+
+    c.Clear();
+    for (unsigned int i=0; i<polys.size(); i++) {
+        ClipperLib::Polygons clipper_clip = tgPolygon::ToClipper( polys[i] );
+        c.AddPolygons(clipper_clip, ClipperLib::ptSubject);
+    }
+    c.Execute(ClipperLib::ctUnion, clipper_result, ClipperLib::pftNonZero, ClipperLib::pftNonZero);
+
+    result = tgPolygon::FromClipper( clipper_result );
+    result = tgPolygon::AddColinearNodes( result, all_nodes );
+
+    return result;
+}
+
 tgPolygon tgPolygon::Diff( const tgPolygon& subject, tgPolygon& clip )
 {
     tgPolygon result;
diff --git a/src/Lib/Polygon/polygon.hxx b/src/Lib/Polygon/polygon.hxx
index c1005e0a..37c1cea8 100644
--- a/src/Lib/Polygon/polygon.hxx
+++ b/src/Lib/Polygon/polygon.hxx
@@ -594,6 +594,7 @@ public:
     static void      SetDump( bool dmp );
     static tgPolygon Union( const tgContour& subject, tgPolygon& clip );
     static tgPolygon Union( const tgPolygon& subject, tgPolygon& clip );
+    static tgPolygon Union( const tgpolygon_list& polys );
     static tgPolygon Diff( const tgPolygon& subject, tgPolygon& clip );
     static tgPolygon Intersect( const tgPolygon& subject, const tgPolygon& clip );