diff --git a/src/Airports/GenAirports850/airport.cxx b/src/Airports/GenAirports850/airport.cxx
index 5135a4ff..40baa3ad 100644
--- a/src/Airports/GenAirports850/airport.cxx
+++ b/src/Airports/GenAirports850/airport.cxx
@@ -517,15 +517,11 @@ void Airport::merge_slivers( superpoly_list& polys, poly_list& slivers_list ) {
 
 void Airport::BuildBtg(const string& root, const string_list& elev_src )
 {
-    ClipPolyType accum;
-    poly_list    slivers;
+    poly_list      slivers;
+    poly_list      line_slivers;
 
-    // try to keep line accumulator in clipper format for speed...
-    ClipPolyType lines;
-    poly_list    line_slivers;
-
-    TGPolygon apt_base;
-    TGPolygon apt_clearing;
+    TGPolygon      apt_base;
+    TGPolygon      apt_clearing;
 
     // runways
     superpoly_list rwy_polys;
@@ -539,7 +535,6 @@ void Airport::BuildBtg(const string& root, const string_list& elev_src )
     superpoly_list line_polys;
     texparams_list line_tps;
 
-    // int i, j, k;
     Point3D p;
 
     bool verbose_triangulation = false;
@@ -594,6 +589,10 @@ void Airport::BuildBtg(const string& root, const string_list& elev_src )
     build_start.stamp();
 
     // Add the linear features
+
+
+    tgPolygonInitClipperAccumulator();
+
     if (features.size())
     {
         for ( unsigned int i=0; i<features.size(); i++ )
@@ -608,7 +607,7 @@ void Airport::BuildBtg(const string& root, const string_list& elev_src )
                 make_shapefiles = false;
             }
 
-            features[i]->BuildBtg( &line_polys, &line_tps, &lines, &rwy_lights, make_shapefiles );
+            features[i]->BuildBtg( &line_polys, &line_tps, &rwy_lights, make_shapefiles );
         }
     }
     else
@@ -616,9 +615,15 @@ void Airport::BuildBtg(const string& root, const string_list& elev_src )
         SG_LOG(SG_GENERAL, SG_DEBUG, "no markings");
     }
 
+    /* DOne with the linear features accumulator */
+    tgPolygonFreeClipperAccumulator();
+
     log_time = time(0);
     SG_LOG( SG_GENERAL, SG_ALERT, "Finished building Linear Features for " << icao << " at " << ctime(&log_time) );
 
+    // Initialize a new accumulator for the other objects
+    tgPolygonInitClipperAccumulator();
+
     // Build runways next
     for ( unsigned int i=0; i<runways.size(); i++ )
     {
@@ -635,11 +640,11 @@ void Airport::BuildBtg(const string& root, const string_list& elev_src )
 
         if (boundary.size())
         {
-            runways[i]->BuildBtg( &rwy_polys, &rwy_tps, &rwy_lights, &accum, slivers, NULL, NULL, make_shapefiles );
+            runways[i]->BuildBtg( &rwy_polys, &rwy_tps, &rwy_lights, slivers, NULL, NULL, make_shapefiles );
         }
         else
         {
-            runways[i]->BuildBtg( &rwy_polys, &rwy_tps, &rwy_lights, &accum, slivers, &apt_base, &apt_clearing, make_shapefiles );
+            runways[i]->BuildBtg( &rwy_polys, &rwy_tps, &rwy_lights, slivers, &apt_base, &apt_clearing, make_shapefiles );
         }
 
         // Now try to merge any slivers we found
@@ -668,11 +673,11 @@ void Airport::BuildBtg(const string& root, const string_list& elev_src )
 
             if (boundary.size())
             {
-                helipads[i]->BuildBtg( &rwy_polys, &rwy_tps, &rwy_lights, &accum, slivers, NULL, NULL );
+                helipads[i]->BuildBtg( &rwy_polys, &rwy_tps, &rwy_lights, slivers, NULL, NULL );
             }
             else
             {
-                helipads[i]->BuildBtg( &rwy_polys, &rwy_tps, &rwy_lights, &accum, slivers, &apt_base, &apt_clearing );
+                helipads[i]->BuildBtg( &rwy_polys, &rwy_tps, &rwy_lights, slivers, &apt_base, &apt_clearing );
             }
 
             // Now try to merge any slivers we found
@@ -698,11 +703,11 @@ void Airport::BuildBtg(const string& root, const string_list& elev_src )
 
             if (boundary.size())
             {
-                pavements[i]->BuildBtg( &pvmt_polys, &pvmt_tps, &accum, slivers, NULL, NULL, make_shapefiles );
+                pavements[i]->BuildBtg( &pvmt_polys, &pvmt_tps, slivers, NULL, NULL, make_shapefiles );
             }
             else
             {
-                pavements[i]->BuildBtg( &pvmt_polys, &pvmt_tps, &accum, slivers, &apt_base, &apt_clearing, make_shapefiles );
+                pavements[i]->BuildBtg( &pvmt_polys, &pvmt_tps, slivers, &apt_base, &apt_clearing, make_shapefiles );
             }
 
             // Now try to merge any slivers we found
@@ -736,11 +741,11 @@ void Airport::BuildBtg(const string& root, const string_list& elev_src )
 
             if (boundary.size())
             {
-                taxiways[i]->BuildBtg( &pvmt_polys, &pvmt_tps, &rwy_lights, &accum, slivers, NULL, NULL, make_shapefiles );
+                taxiways[i]->BuildBtg( &pvmt_polys, &pvmt_tps, &rwy_lights, slivers, NULL, NULL, make_shapefiles );
             }
             else
             {
-                taxiways[i]->BuildBtg( &pvmt_polys, &pvmt_tps, &rwy_lights, &accum, slivers, &apt_base, &apt_clearing, make_shapefiles );
+                taxiways[i]->BuildBtg( &pvmt_polys, &pvmt_tps, &rwy_lights, slivers, &apt_base, &apt_clearing, make_shapefiles );
             }
 
             // Now try to merge any slivers we found
@@ -765,11 +770,11 @@ void Airport::BuildBtg(const string& root, const string_list& elev_src )
 
             if (boundary.size())
             {
-                runways[i]->BuildShoulder( &rwy_polys, &rwy_tps, &accum, slivers, NULL, NULL );
+                runways[i]->BuildShoulder( &rwy_polys, &rwy_tps, slivers, NULL, NULL );
             }
             else
             {
-                runways[i]->BuildShoulder( &rwy_polys, &rwy_tps, &accum, slivers, &apt_base, &apt_clearing );
+                runways[i]->BuildShoulder( &rwy_polys, &rwy_tps, slivers, &apt_base, &apt_clearing );
             }
 
             // Now try to merge any slivers we found
@@ -789,11 +794,11 @@ void Airport::BuildBtg(const string& root, const string_list& elev_src )
 
             if (boundary.size())
             {
-                helipads[i]->BuildShoulder( &rwy_polys, &rwy_tps, &accum, slivers, NULL, NULL );
+                helipads[i]->BuildShoulder( &rwy_polys, &rwy_tps, slivers, NULL, NULL );
             }
             else
             {
-                helipads[i]->BuildShoulder( &rwy_polys, &rwy_tps, &accum, slivers, &apt_base, &apt_clearing );
+                helipads[i]->BuildShoulder( &rwy_polys, &rwy_tps, slivers, &apt_base, &apt_clearing );
             }
 
             // Now try to merge any slivers we found
@@ -821,7 +826,7 @@ void Airport::BuildBtg(const string& root, const string_list& elev_src )
 
     TGPolygon filled_base  = tgPolygonStripHoles( apt_base );
     TGPolygon divided_base = tgPolygonSplitLongEdges( filled_base, 200.0 );
-    TGPolygon base_poly    = tgPolygonDiffClipper( divided_base, accum );
+    TGPolygon base_poly    = tgPolygonDiffClipperWithAccumulator( divided_base );
 
     build_end.stamp();
     build_time = build_end - build_start;
diff --git a/src/Airports/GenAirports850/closedpoly.cxx b/src/Airports/GenAirports850/closedpoly.cxx
index c19f4c7f..20138db1 100644
--- a/src/Airports/GenAirports850/closedpoly.cxx
+++ b/src/Airports/GenAirports850/closedpoly.cxx
@@ -380,10 +380,9 @@ void ClosedPoly::Finish()
     holes.clear();
 }
 
-int ClosedPoly::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, ClipPolyType* accum, poly_list& slivers, TGPolygon* apt_base, TGPolygon* apt_clearing, bool make_shapefiles )
+int ClosedPoly::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, poly_list& slivers, TGPolygon* apt_base, TGPolygon* apt_clearing, bool make_shapefiles )
 {
     TGPolygon base, safe_base;
-    TGPolygon pre_accum;
 
     string    material;
     void*     ds_id = NULL;        // If we are going to build shapefiles
@@ -446,11 +445,9 @@ int ClosedPoly::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams,
                 l_id = tgShapefileOpenLayer( ds_id, layer_name );
                 sprintf( feature_name, "original" );
                 tgShapefileCreateFeature( ds_id, l_id, pre_tess, feature_name );
-
-                pre_accum = *accum;
             }
     
-            TGPolygon clipped = tgPolygonDiffClipper( pre_tess, *accum );
+            TGPolygon clipped = tgPolygonDiffClipperWithAccumulator( pre_tess );
             tgPolygonFindSlivers( clipped, slivers );
 
             SG_LOG(SG_GENERAL, SG_DEBUG, "clipped = " << clipped.contours());
@@ -462,7 +459,7 @@ int ClosedPoly::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams,
 
             rwy_polys->push_back( sp );
 
-            *accum = tgPolygonUnionClipper( pre_tess, *accum );
+            tgPolygonAddToClipperAccumulator( pre_tess, false );
 
             /* If debugging this poly, write the poly, and clipped poly and the accum buffer into their own layers */
             if ( make_shapefiles ) {
@@ -473,16 +470,6 @@ int ClosedPoly::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams,
                 l_id = tgShapefileOpenLayer( ds_id, layer_name );
                 sprintf( feature_name, "clipped" );
                 tgShapefileCreateFeature( ds_id, l_id, clipped, feature_name );
-
-                sprintf( layer_name, "pre_accum" );
-                l_id = tgShapefileOpenLayer( ds_id, layer_name );
-                sprintf( feature_name, "pre_accum" );
-                tgShapefileCreateFeature( ds_id, l_id, pre_accum, feature_name );
-
-                sprintf( layer_name, "post_accum" );
-                l_id = tgShapefileOpenLayer( ds_id, layer_name );
-                sprintf( feature_name, "post_accum" );
-                tgShapefileCreateFeature( ds_id, l_id, *accum, feature_name );
             }
 
             SG_LOG(SG_GENERAL, SG_DEBUG, "tp construct");
diff --git a/src/Airports/GenAirports850/closedpoly.hxx b/src/Airports/GenAirports850/closedpoly.hxx
index 8f1afd48..c9d4c01f 100644
--- a/src/Airports/GenAirports850/closedpoly.hxx
+++ b/src/Airports/GenAirports850/closedpoly.hxx
@@ -28,7 +28,7 @@ public:
     int  BuildBtg( TGPolygon* apt_base, TGPolygon* apt_clearing, bool make_shapefiles );
 
     // Build BTG for pavements for airports with no boundary
-    int  BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, ClipPolyType* accum, poly_list& slivers, TGPolygon* apt_base, TGPolygon* apt_clearing, bool make_shapefiles );
+    int  BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, poly_list& slivers, TGPolygon* apt_base, TGPolygon* apt_clearing, bool make_shapefiles );
 
     FeatureList* GetFeatures()
     {
diff --git a/src/Airports/GenAirports850/helipad.cxx b/src/Airports/GenAirports850/helipad.cxx
index 7516c1e6..e1d0184a 100644
--- a/src/Airports/GenAirports850/helipad.cxx
+++ b/src/Airports/GenAirports850/helipad.cxx
@@ -88,11 +88,10 @@ superpoly_list Helipad::gen_helipad_lights(double maxsize){
 
 void Helipad::WriteGeom( TGPolygon polygon, string material,
                         superpoly_list *rwy_polys,
-                        ClipPolyType *accum,
                         poly_list& slivers )
 {
     // Clip the new polygon against what ever has already been created.
-    TGPolygon clipped = tgPolygonDiffClipper( polygon, *accum );
+    TGPolygon clipped = tgPolygonDiffClipperWithAccumulator( polygon );
     tgPolygonFindSlivers( clipped, slivers );
 
     // Split long edges to create an object that can better flow with
@@ -107,13 +106,12 @@ void Helipad::WriteGeom( TGPolygon polygon, string material,
     sp.set_material( material );
     rwy_polys->push_back( sp );
 
-    *accum = tgPolygonUnionClipper( polygon, *accum );
+    tgPolygonAddToClipperAccumulator( polygon, false );
 }
 
 void Helipad::BuildBtg( superpoly_list *rwy_polys,
                         texparams_list *texparams,
                         superpoly_list *rwy_lights,
-                        ClipPolyType *accum, 
                         poly_list& slivers, 
                         TGPolygon* apt_base, 
                         TGPolygon* apt_clearing )
@@ -143,7 +141,7 @@ void Helipad::BuildBtg( superpoly_list *rwy_polys,
     else
         material = "pc_";
     // write out
-    WriteGeom( helipad, material + "heli", rwy_polys, accum, slivers);
+    WriteGeom( helipad, material + "heli", rwy_polys, slivers);
 
     TGTexParams tp;
     tp = TGTexParams( helipad.get_pt(0,0).toSGGeod(), maxsize, maxsize, heli.heading );
@@ -185,7 +183,7 @@ void Helipad::BuildBtg( superpoly_list *rwy_polys,
         TGPolygon area_geom;
         for (i = 0; i < 2; ++i) {
             area_geom.add_contour(area_poly.get_contour(i), false);
-            WriteGeom( area_geom, material + "tiedown", rwy_polys, accum, slivers);
+            WriteGeom( area_geom, material + "tiedown", rwy_polys, slivers);
 
             tp = TGTexParams( area_poly.get_pt(i,0).toSGGeod(), maxsize, areahight, heading );
             tp.set_minu( 1 );
@@ -277,7 +275,6 @@ void Helipad::BuildBtg( superpoly_list *rwy_polys,
 
 void Helipad::BuildShoulder( superpoly_list *rwy_polys,
                              texparams_list *texparams,
-                             ClipPolyType *accum,
                              poly_list& slivers,
                              TGPolygon* apt_base,
                              TGPolygon* apt_clearing )
@@ -289,7 +286,7 @@ void Helipad::BuildShoulder( superpoly_list *rwy_polys,
         shoulder = shoulder_polys[i].get_poly();
 
         // Clip the new polygon against what ever has already been created.
-        TGPolygon clipped = tgPolygonDiffClipper( shoulder, *accum );
+        TGPolygon clipped = tgPolygonDiffClipperWithAccumulator( shoulder );
         tgPolygonFindSlivers( clipped, slivers );
 
         // Split long edges to create an object that can better flow with
@@ -300,7 +297,7 @@ void Helipad::BuildShoulder( superpoly_list *rwy_polys,
         rwy_polys->push_back( shoulder_polys[i] );
         texparams->push_back( shoulder_tps[i] );
 
-        *accum = tgPolygonUnionClipper( shoulder, *accum );
+        tgPolygonAddToClipperAccumulator( shoulder, false );
 
         if (apt_base)
         {
diff --git a/src/Airports/GenAirports850/helipad.hxx b/src/Airports/GenAirports850/helipad.hxx
index 23a7197b..c91259f4 100644
--- a/src/Airports/GenAirports850/helipad.hxx
+++ b/src/Airports/GenAirports850/helipad.hxx
@@ -24,7 +24,7 @@ class Helipad
 {
 public:
     Helipad(char* def);
-    void BuildBtg( superpoly_list* heli_polys, texparams_list* texparams, superpoly_list* heli_lights, ClipPolyType* accum, poly_list& slivers, TGPolygon* apt_base, TGPolygon* apt_clearing );
+    void BuildBtg( superpoly_list* heli_polys, texparams_list* texparams, superpoly_list* heli_lights, poly_list& slivers, TGPolygon* apt_base, TGPolygon* apt_clearing );
 
     SGGeod GetLoc()
     {
@@ -38,7 +38,6 @@ public:
 
     void BuildShoulder( superpoly_list *rwy_polys,
                         texparams_list *texparams,
-                        ClipPolyType *accum,
                         poly_list& slivers,
                         TGPolygon* apt_base,
                         TGPolygon* apt_clearing );
@@ -78,7 +77,6 @@ private:
 
     void WriteGeom( TGPolygon polygon, string material,
                         superpoly_list *rwy_polys,
-                        ClipPolyType *accum,
                         poly_list& slivers );
 
 };
diff --git a/src/Airports/GenAirports850/linearfeature.cxx b/src/Airports/GenAirports850/linearfeature.cxx
index f7d8b4c7..3639f2b8 100644
--- a/src/Airports/GenAirports850/linearfeature.cxx
+++ b/src/Airports/GenAirports850/linearfeature.cxx
@@ -844,7 +844,7 @@ int LinearFeature::Finish( bool closed, unsigned int idx )
     return 1;
 }
 
-int LinearFeature::BuildBtg(superpoly_list* line_polys, texparams_list* line_tps, ClipPolyType* lines, superpoly_list* lights, bool make_shapefiles )
+int LinearFeature::BuildBtg(superpoly_list* line_polys, texparams_list* line_tps, superpoly_list* lights, bool make_shapefiles )
 {
     TGPolygon poly, tmp;
     void*     ds_id = NULL;        // If we are going to build shapefiles
@@ -860,27 +860,12 @@ int LinearFeature::BuildBtg(superpoly_list* line_polys, texparams_list* line_tps
     SG_LOG(SG_GENERAL, SG_DEBUG, "\nLinearFeature::BuildBtg: " << description);
     for ( unsigned int i = 0; i < marking_polys.size(); i++)
     {
-        poly = marking_polys[i].get_poly();
-        poly.get_bounding_box(minp, maxp);
-        tg::Rectangle box1(minp, maxp);
-
-        for (int j= 0; j < lines->contours(); ++j)
-        {
-            tmp.erase();
-            tmp.add_contour(lines->get_contour(j), 0);
-            tmp.get_bounding_box(min, max);
-            tg::Rectangle box2(min, max);
-
-            if ( box2.intersects(box1) )
-            {
-                poly = tgPolygonDiffClipper( poly, tmp );
-            }
-        }
+        poly = tgPolygonDiffClipperWithAccumulator( marking_polys[i].get_poly() );
 
         marking_polys[i].set_poly( poly );
         line_polys->push_back( marking_polys[i] );
 
-        /* If debugging this lf, write the poly, and the accum buffer at each step into their own layers */
+        /* If debugging this lf, write the polys into their own layers */
         if (ds_id) {
             char layer_name[128];
             sprintf( layer_name, "poly_%d", i );
@@ -889,15 +874,9 @@ int LinearFeature::BuildBtg(superpoly_list* line_polys, texparams_list* line_tps
             char feature_name[128];
             sprintf( feature_name, "poly_%d", i);
             tgShapefileCreateFeature( ds_id, l_id, poly, feature_name );
-
-            sprintf( layer_name, "accum_%d", i );
-            l_id = tgShapefileOpenLayer( ds_id, layer_name );
-
-            sprintf( feature_name, "accum_%d", i );
-            tgShapefileCreateFeature( ds_id, l_id, *lines, feature_name );
         }
 
-        lines->add_contour(poly.get_contour(0), 0);
+        tgPolygonAddToClipperAccumulator(poly, false);
 
         line_tps->push_back( marking_tps[i] );
     }
diff --git a/src/Airports/GenAirports850/linearfeature.hxx b/src/Airports/GenAirports850/linearfeature.hxx
index 1a1f2981..16b291c0 100644
--- a/src/Airports/GenAirports850/linearfeature.hxx
+++ b/src/Airports/GenAirports850/linearfeature.hxx
@@ -97,7 +97,7 @@ public:
     }
 
     int Finish( bool closed, unsigned int idx );
-    int BuildBtg( superpoly_list* line_polys, texparams_list* line_tps, ClipPolyType* lines, superpoly_list* lights, bool debug );
+    int BuildBtg( superpoly_list* line_polys, texparams_list* line_tps, superpoly_list* lights, bool debug );
 //    int BuildBtg( float alt_m, superpoly_list* line_polys, texparams_list* line_tps, ClipPolyType* line_accum, superpoly_list* lights ); 
 
 private:
diff --git a/src/Airports/GenAirports850/runway.cxx b/src/Airports/GenAirports850/runway.cxx
index 8e245955..301dc7c9 100644
--- a/src/Airports/GenAirports850/runway.cxx
+++ b/src/Airports/GenAirports850/runway.cxx
@@ -89,7 +89,7 @@ point_list WaterRunway::GetNodes()
 }
 
 
-int Runway::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, superpoly_list* rwy_lights, ClipPolyType* accum, poly_list& slivers, TGPolygon* apt_base, TGPolygon* apt_clearing, bool make_shapefiles )
+int Runway::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, superpoly_list* rwy_lights, poly_list& slivers, TGPolygon* apt_base, TGPolygon* apt_clearing, bool make_shapefiles )
 {
     TGPolygon base, safe_base;
 
@@ -137,7 +137,7 @@ int Runway::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, supe
         case 1: // asphalt:
         case 2: // concrete
             SG_LOG( SG_GENERAL, SG_DEBUG, "Build Runway: asphalt or concrete " << rwy.surface);
-            gen_rwy( rwy_polys, texparams, accum, slivers, make_shapefiles );
+            gen_rwy( rwy_polys, texparams, slivers, make_shapefiles );
             gen_runway_lights( rwy_lights );
             break;
     
@@ -146,7 +146,7 @@ int Runway::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, supe
         case 5: // Gravel
         case 12: // dry lakebed
             SG_LOG( SG_GENERAL, SG_DEBUG, "Build Runway: Grass, Dirt, Gravel or Dry Lakebed " << rwy.surface );
-            gen_simple_rwy( rwy_polys, texparams, accum, slivers );
+            gen_simple_rwy( rwy_polys, texparams, slivers );
             gen_runway_lights( rwy_lights );
             break;
 
diff --git a/src/Airports/GenAirports850/runway.hxx b/src/Airports/GenAirports850/runway.hxx
index 5f1ccc71..052fd623 100644
--- a/src/Airports/GenAirports850/runway.hxx
+++ b/src/Airports/GenAirports850/runway.hxx
@@ -42,7 +42,6 @@ public:
     int BuildBtg( superpoly_list* rwy_polys, 
                   texparams_list* texparams, 
                   superpoly_list* rwy_lights, 
-                  ClipPolyType* accum, 
                   poly_list& slivers, 
                   TGPolygon* apt_base, 
                   TGPolygon* apt_clearing,
@@ -50,7 +49,6 @@ public:
 
     void BuildShoulder( superpoly_list *rwy_polys,
                         texparams_list *texparams,
-                        ClipPolyType *accum,
                         poly_list& slivers, 
                         TGPolygon* apt_base, 
                         TGPolygon* apt_clearing );
@@ -108,7 +106,6 @@ private:
                              double &start_pct, double &end_pct,
                              superpoly_list* rwy_polys,
                              texparams_list* texparams,
-                             ClipPolyType* accum,
                              poly_list& slivers,
                              bool make_shapefiles );
 
@@ -123,7 +120,6 @@ private:
                       texparams_list *texparams,
                       superpoly_list *shoulder_polys,
                       texparams_list *shoulder_tps,
-                      ClipPolyType *accum,
                       poly_list& slivers,
                       bool make_shapefiles );
 
@@ -136,11 +132,10 @@ private:
                                std::string surface, 
                                TGSuperPoly& sp, TGTexParams& tp );
 
-    void gen_simple_rwy( superpoly_list *rwy_polys, texparams_list *texparams, ClipPolyType *accum, poly_list& slivers );
+    void gen_simple_rwy( superpoly_list *rwy_polys, texparams_list *texparams, poly_list& slivers );
     
     void gen_rwy( superpoly_list* rwy_polys,
                   texparams_list* texparams,
-                  ClipPolyType* accum,
                   poly_list& slivers,
                   bool make_shapefiles );
 
diff --git a/src/Airports/GenAirports850/rwy_gen.cxx b/src/Airports/GenAirports850/rwy_gen.cxx
index e8aaa349..240c7ea3 100644
--- a/src/Airports/GenAirports850/rwy_gen.cxx
+++ b/src/Airports/GenAirports850/rwy_gen.cxx
@@ -156,7 +156,6 @@ void Runway::gen_runway_section( const TGPolygon& runway,
                                  texparams_list *texparams,
                                  superpoly_list *shoulder_polys,
                                  texparams_list *shoulder_tps,
-                                 ClipPolyType *accum,
                                  poly_list& slivers,
                                  bool make_shapefiles ) 
 {
@@ -360,7 +359,7 @@ void Runway::gen_runway_section( const TGPolygon& runway,
     }
 
     // Clip the new polygon against what ever has already been created.
-    TGPolygon clipped = tgPolygonDiffClipper( section, *accum );
+    TGPolygon clipped = tgPolygonDiffClipperWithAccumulator( section );
     tgPolygonFindSlivers( clipped, slivers );
 
     // Split long edges to create an object that can better flow with
@@ -377,7 +376,7 @@ void Runway::gen_runway_section( const TGPolygon& runway,
 
     SG_LOG(SG_GENERAL, SG_DEBUG, "section = " << clipped.contours());
 
-    *accum = tgPolygonUnionClipper( section, *accum );
+    tgPolygonAddToClipperAccumulator( section, false );
 
     // Store away what we need to know for texture coordinate
     // calculation.  (CLO 10/20/02: why can't we calculate texture
@@ -419,7 +418,6 @@ void Runway::gen_rw_designation( TGPolygon poly, double heading, string rwname,
                                  double &start_pct, double &end_pct,
                                  superpoly_list *rwy_polys,
                                  texparams_list *texparams,
-                                 ClipPolyType *accum,
                                  poly_list& slivers,
                                  bool make_shapefiles )
 {
@@ -447,7 +445,7 @@ void Runway::gen_rw_designation( TGPolygon poly, double heading, string rwname,
                                 letter,
                                 rwy_polys, texparams, 
                                 &shoulder_polys, &shoulder_tps,
-                                accum, slivers,
+                                slivers,
                                 make_shapefiles );
         }
 
@@ -477,7 +475,7 @@ void Runway::gen_rw_designation( TGPolygon poly, double heading, string rwname,
                                 tex1,
                                 rwy_polys, texparams, 
                                 &shoulder_polys, &shoulder_tps,
-                                accum, slivers,
+                                slivers,
                                 make_shapefiles );
             gen_runway_section( poly,
                                 start_pct, end_pct,
@@ -487,7 +485,7 @@ void Runway::gen_rw_designation( TGPolygon poly, double heading, string rwname,
                                 tex2,
                                 rwy_polys, texparams, 
                                 &shoulder_polys, &shoulder_tps,
-                                accum, slivers,
+                                slivers,
                                 make_shapefiles );
 
         } else if (rwname.length() == 1) {
@@ -501,7 +499,7 @@ void Runway::gen_rw_designation( TGPolygon poly, double heading, string rwname,
                                 tex1,
                                 rwy_polys, texparams, 
                                 &shoulder_polys, &shoulder_tps,
-                                accum, slivers,
+                                slivers,
                                 make_shapefiles );
         }
     }
@@ -513,7 +511,6 @@ void Runway::gen_rw_designation( TGPolygon poly, double heading, string rwname,
 // document AC 150/5340-1H
 void Runway::gen_rwy( superpoly_list *rwy_polys,
                       texparams_list *texparams,
-                      ClipPolyType *accum,
                       poly_list& slivers,
                       bool make_shapefiles )
 {
@@ -619,7 +616,7 @@ void Runway::gen_rwy( superpoly_list *rwy_polys,
                                     "dspl_thresh",
                                     rwy_polys, texparams,
                                     &shoulder_polys, &shoulder_tps,
-                                    accum, slivers,
+                                    slivers,
                                     make_shapefiles );
 
                 // main chunks
@@ -634,7 +631,7 @@ void Runway::gen_rwy( superpoly_list *rwy_polys,
                                         "dspl_thresh",
                                         rwy_polys, texparams,
                                         &shoulder_polys, &shoulder_tps,
-                                        accum, slivers,
+                                        slivers,
                                         make_shapefiles );
                 }
             }
@@ -650,7 +647,7 @@ void Runway::gen_rwy( superpoly_list *rwy_polys,
                             "dspl_arrows",
                             rwy_polys, texparams, 
                             &shoulder_polys, &shoulder_tps,
-                            accum, slivers,
+                            slivers,
                             make_shapefiles );
         }
 
@@ -666,7 +663,7 @@ void Runway::gen_rwy( superpoly_list *rwy_polys,
                                 "no_threshold",
                                 rwy_polys, texparams, 
                                 &shoulder_polys, &shoulder_tps,
-                                accum, slivers,
+                                slivers,
                                 make_shapefiles );
         } else {
             // Thresholds for all others
@@ -680,14 +677,14 @@ void Runway::gen_rwy( superpoly_list *rwy_polys,
                                 "threshold",
                                 rwy_polys, texparams, 
                                 &shoulder_polys, &shoulder_tps,
-                                accum, slivers,
+                                slivers,
                                 make_shapefiles );
         }
 
         // Runway designation block
         gen_rw_designation( runway_half, heading,
                             rwname, start1_pct, end1_pct, 
-                            rwy_polys, texparams, accum, slivers,
+                            rwy_polys, texparams, slivers,
                             make_shapefiles );
 
         // Generate remaining markings depending on type of runway
@@ -728,7 +725,7 @@ void Runway::gen_rwy( superpoly_list *rwy_polys,
                                         rw_marking_list[i].tex,
                                         rwy_polys, texparams, 
                                         &shoulder_polys, &shoulder_tps,
-                                        accum, slivers,
+                                        slivers,
                                         make_shapefiles );
                 }
             }
@@ -757,7 +754,7 @@ void Runway::gen_rwy( superpoly_list *rwy_polys,
                                 "rest",
                                 rwy_polys, texparams, 
                                 &shoulder_polys, &shoulder_tps,
-                                accum, slivers,
+                                slivers,
                                 make_shapefiles );
         }
 
@@ -787,7 +784,7 @@ void Runway::gen_rwy( superpoly_list *rwy_polys,
                                     "stopway",
                                     rwy_polys, texparams,
                                     &shoulder_polys, &shoulder_tps,
-                                    accum, slivers,
+                                    slivers,
                                     make_shapefiles );
             }
         }
@@ -796,7 +793,6 @@ void Runway::gen_rwy( superpoly_list *rwy_polys,
 
 void Runway::BuildShoulder( superpoly_list *rwy_polys,
                             texparams_list *texparams,
-                            ClipPolyType *accum,
                             poly_list& slivers, 
                             TGPolygon* apt_base, 
                             TGPolygon* apt_clearing )
@@ -808,7 +804,7 @@ void Runway::BuildShoulder( superpoly_list *rwy_polys,
         shoulder = shoulder_polys[i].get_poly();
 
         // Clip the new polygon against what ever has already been created.
-        TGPolygon clipped = tgPolygonDiffClipper( shoulder, *accum );
+        TGPolygon clipped = tgPolygonDiffClipperWithAccumulator( shoulder );
         tgPolygonFindSlivers( clipped, slivers );
 
         // Split long edges to create an object that can better flow with
@@ -819,7 +815,7 @@ void Runway::BuildShoulder( superpoly_list *rwy_polys,
         rwy_polys->push_back( shoulder_polys[i] );
         texparams->push_back( shoulder_tps[i] );
 
-        *accum = tgPolygonUnionClipper( shoulder, *accum );
+        tgPolygonAddToClipperAccumulator( shoulder, false );
 
         if (apt_base)
         {
diff --git a/src/Airports/GenAirports850/rwy_simple.cxx b/src/Airports/GenAirports850/rwy_simple.cxx
index b9c53714..03507b3a 100644
--- a/src/Airports/GenAirports850/rwy_simple.cxx
+++ b/src/Airports/GenAirports850/rwy_simple.cxx
@@ -34,7 +34,6 @@ using std::string;
 // texparams, and accum
 void Runway::gen_simple_rwy( superpoly_list *rwy_polys,
                              texparams_list *texparams,
-                             ClipPolyType *accum,
                              poly_list& slivers )
 {
     TGPolygon runway = gen_runway_w_mid( 0.0, 0.0 );
@@ -91,7 +90,7 @@ void Runway::gen_simple_rwy( superpoly_list *rwy_polys,
                                         "",
                                         rwy_polys, texparams, 
                                         NULL, NULL,
-                                        accum, slivers,
+                                        slivers,
                                         false );
         }
         
@@ -104,7 +103,7 @@ void Runway::gen_simple_rwy( superpoly_list *rwy_polys,
                                     "",
                                     rwy_polys, texparams, 
                                     NULL, NULL,
-                                    accum, slivers,
+                                    slivers,
                                     false );
     }
 }
diff --git a/src/Airports/GenAirports850/taxiway.cxx b/src/Airports/GenAirports850/taxiway.cxx
index 3a134fde..6536ef2c 100644
--- a/src/Airports/GenAirports850/taxiway.cxx
+++ b/src/Airports/GenAirports850/taxiway.cxx
@@ -58,11 +58,10 @@ Taxiway::Taxiway(char* definition)
     lon = pt_x;
 } 
 
-int Taxiway::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, superpoly_list* rwy_lights, ClipPolyType* accum, poly_list& slivers, TGPolygon* apt_base, TGPolygon* apt_clearing, bool make_shapefiles )
+int Taxiway::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, superpoly_list* rwy_lights, poly_list& slivers, TGPolygon* apt_base, TGPolygon* apt_clearing, bool make_shapefiles )
 {
     TGPolygon taxi;
     TGPolygon base, safe_base;
-    TGPolygon pre_accum;
     std::string material;
     void*     ds_id = NULL;        // If we are going to build shapefiles
     void*     l_id  = NULL;        // datasource and layer IDs
@@ -133,11 +132,9 @@ int Taxiway::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, sup
         l_id = tgShapefileOpenLayer( ds_id, layer_name );
         sprintf( feature_name, "original" );
         tgShapefileCreateFeature( ds_id, l_id, taxi, feature_name );
-
-        pre_accum = *accum;
     }
-    
-    TGPolygon clipped = tgPolygonDiffClipper( taxi, *accum );
+
+    TGPolygon clipped = tgPolygonDiffClipperWithAccumulator( taxi );
     tgPolygonFindSlivers( clipped, slivers );
 
     SG_LOG(SG_GENERAL, SG_DEBUG, "clipped = " << clipped.contours());
@@ -149,7 +146,7 @@ int Taxiway::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, sup
 
     rwy_polys->push_back( sp );
 
-    *accum = tgPolygonUnionClipper( taxi, *accum );
+    tgPolygonAddToClipperAccumulator( taxi, false );
 
     /* If debugging this poly, write the poly, and clipped poly and the accum buffer into their own layers */
     if ( make_shapefiles ) {
@@ -160,16 +157,6 @@ int Taxiway::BuildBtg( superpoly_list* rwy_polys, texparams_list* texparams, sup
         l_id = tgShapefileOpenLayer( ds_id, layer_name );
         sprintf( feature_name, "clipped" );
         tgShapefileCreateFeature( ds_id, l_id, clipped, feature_name );
-
-        sprintf( layer_name, "pre_accum" );
-        l_id = tgShapefileOpenLayer( ds_id, layer_name );
-        sprintf( feature_name, "pre_accum" );
-        tgShapefileCreateFeature( ds_id, l_id, pre_accum, feature_name );
-
-        sprintf( layer_name, "post_accum" );
-        l_id = tgShapefileOpenLayer( ds_id, layer_name );
-        sprintf( feature_name, "post_accum" );
-        tgShapefileCreateFeature( ds_id, l_id, *accum, feature_name );
     }
 
     SG_LOG(SG_GENERAL, SG_DEBUG, "tp construct");
diff --git a/src/Airports/GenAirports850/taxiway.hxx b/src/Airports/GenAirports850/taxiway.hxx
index 76009f5a..9fa820ac 100644
--- a/src/Airports/GenAirports850/taxiway.hxx
+++ b/src/Airports/GenAirports850/taxiway.hxx
@@ -22,7 +22,6 @@ public:
     int BuildBtg( superpoly_list* taxi_polys, 
                   texparams_list* texparams, 
                   superpoly_list* taxi_lights, 
-                  ClipPolyType* accum, 
                   poly_list& slivers, 
                   TGPolygon* apt_base, 
                   TGPolygon* apt_clearing,