diff --git a/src/BuildTiles/Main/tgconstruct_math.cxx b/src/BuildTiles/Main/tgconstruct_math.cxx
index bbbc905b..c3773068 100644
--- a/src/BuildTiles/Main/tgconstruct_math.cxx
+++ b/src/BuildTiles/Main/tgconstruct_math.cxx
@@ -53,15 +53,11 @@ SGVec3d TGConstruct::calc_normal( double area, Point3D p1, Point3D p2, Point3D p
     const double area_eps = 1.0e-12;
     if ( area < area_eps ) {
         degenerate = true;
-    }
-
-    if ( fabs(p1.x() - p2.x()) < SG_EPSILON && fabs(p1.x() - p3.x()) < SG_EPSILON ) {
+    } else if ( fabs(p1.x() - p2.x()) < SG_EPSILON && fabs(p1.x() - p3.x()) < SG_EPSILON ) {
         degenerate = true;
-    }
-    if ( fabs(p1.y() - p2.y()) < SG_EPSILON && fabs(p1.y() - p3.y()) < SG_EPSILON ) {
+    } else if ( fabs(p1.y() - p2.y()) < SG_EPSILON && fabs(p1.y() - p3.y()) < SG_EPSILON ) {
         degenerate = true;
-    }
-    if ( fabs(p1.z() - p2.z()) < SG_EPSILON && fabs(p1.z() - p3.z()) < SG_EPSILON ) {
+    } else if ( fabs(p1.z() - p2.z()) < SG_EPSILON && fabs(p1.z() - p3.z()) < SG_EPSILON ) {
         degenerate = true;
     }
 
diff --git a/src/BuildTiles/Main/tgshape.cxx b/src/BuildTiles/Main/tgshape.cxx
index 1555f884..540dadd9 100644
--- a/src/BuildTiles/Main/tgshape.cxx
+++ b/src/BuildTiles/Main/tgshape.cxx
@@ -43,13 +43,15 @@ void TGShape::SetMask( TGPolygon mask )
 void TGShape::BuildMask( void )
 {
     TGPolygon poly;
+    poly_list polys;
     clip_mask.erase();
 
     for (unsigned int i=0; i<sps.size(); i++)
     {
-        poly = sps[i].get_poly();
-        clip_mask = tgPolygonUnion( clip_mask, poly );
+        polys.push_back( sps[i].get_poly() );
     }
+
+    clip_mask = tgPolygonUnion( polys );
 }
 
 void TGShape::IntersectPolys( void )
diff --git a/src/Lib/Geometry/poly_support.hxx b/src/Lib/Geometry/poly_support.hxx
index a1c35c4c..f0e66ea8 100644
--- a/src/Lib/Geometry/poly_support.hxx
+++ b/src/Lib/Geometry/poly_support.hxx
@@ -41,13 +41,11 @@
 
 
 // Calculate the area of a triangle
-inline double triangle_area( const Point3D p1,
-			     const Point3D p2,
-			     const Point3D p3 )
+inline double triangle_area( const Point3D& p1, const Point3D& p2, const Point3D& p3 )
 {
     return fabs(0.5 * ( p1.x() * p2.y() - p2.x() * p1.y() +
-			p2.x() * p3.y() - p3.x() * p2.y() +
-			p3.x() * p1.y() - p1.x() * p3.y() ));
+                        p2.x() * p3.y() - p3.x() * p2.y() +
+                        p3.x() * p1.y() - p1.x() * p3.y() ));
 }
 
 
diff --git a/src/Lib/Polygon/polygon.cxx b/src/Lib/Polygon/polygon.cxx
index e9b1c794..edc3cd29 100644
--- a/src/Lib/Polygon/polygon.cxx
+++ b/src/Lib/Polygon/polygon.cxx
@@ -567,7 +567,7 @@ TGPolygon polygon_clip_clipper( clip_op poly_op, const TGPolygon& subject, const
     } else if ( poly_op == POLY_XOR ) {
         op = ClipperLib::ctXor;
     } else if ( poly_op == POLY_UNION ) {
-    	op = ClipperLib::ctUnion;
+        op = ClipperLib::ctUnion;
     } else {
         throw sg_exception("Unknown polygon op, exiting.");
     }
@@ -581,7 +581,7 @@ TGPolygon polygon_clip_clipper( clip_op poly_op, const TGPolygon& subject, const
 
     make_tg_poly_from_clipper( clipper_result, &result );
 
-	return result;
+    return result;
 }
 
 
@@ -605,6 +605,24 @@ TGPolygon tgPolygonUnion( const TGPolygon& subject, const TGPolygon& clip ) {
     return polygon_clip_clipper( POLY_UNION, subject, clip );
 }
 
+TGPolygon tgPolygonUnion( const poly_list& clips )
+{
+    ClipperLib::Polygons clipper_result;
+    ClipperLib::Clipper c;
+    TGPolygon result;
+
+    c.Clear();
+    for (unsigned int i=0; i<clips.size(); i++) {
+        ClipperLib::Polygons clipper_clip;
+        make_clipper_poly( clips[i], &clipper_clip );
+        c.AddPolygons(clipper_clip, ClipperLib::ptClip);
+    }
+    c.Execute(ClipperLib::ctUnion, clipper_result, ClipperLib::pftEvenOdd, ClipperLib::pftEvenOdd);
+
+    make_tg_poly_from_clipper( clipper_result, &result );
+
+    return result;
+}
 
 
 
diff --git a/src/Lib/Polygon/polygon.hxx b/src/Lib/Polygon/polygon.hxx
index c3ca5a2f..31a8e1d2 100644
--- a/src/Lib/Polygon/polygon.hxx
+++ b/src/Lib/Polygon/polygon.hxx
@@ -258,6 +258,7 @@ TGPolygon tgPolygonXor( const TGPolygon& subject, const TGPolygon& clip );
 
 // Union
 TGPolygon tgPolygonUnion( const TGPolygon& subject, const TGPolygon& clip );
+TGPolygon tgPolygonUnion( const poly_list& clips );
 
 // wrapper for clipper clip routines