projection: fallback to 'large thin box' if intersection with plane fails.

also implement SVG debugging output for 2d + 3d Nef Polyhedrons.

6 files changed, 396 insertions, 70 deletions

diff --git a/src/CGAL_Nef_polyhedron.h b/src/CGAL_Nef_polyhedron.h
index 694b420..3157ff2 100644
--- a/src/CGAL_Nef_polyhedron.h
+++ b/src/CGAL_Nef_polyhedron.h
@@ -20,7 +20,8 @@ public:
 	CGAL_Nef_polyhedron &operator-=(const CGAL_Nef_polyhedron &other);
 	CGAL_Nef_polyhedron &minkowski(const CGAL_Nef_polyhedron &other);
 	CGAL_Nef_polyhedron copy() const;
-	std::string dump_p2() const;
+	std::string dump_svg() const;
+	std::string dump() const;
 	int weight() const;
 	class PolySet *convertToPolyset();
 	class DxfData *convertToDxfData() const;
diff --git a/src/CGAL_Nef_polyhedron_DxfData.cc b/src/CGAL_Nef_polyhedron_DxfData.cc
index 411a340..922a7ec 100644
--- a/src/CGAL_Nef_polyhedron_DxfData.cc
+++ b/src/CGAL_Nef_polyhedron_DxfData.cc
@@ -28,6 +28,7 @@
 #include "grid.h"
 #include "CGAL_Nef_polyhedron.h"
 #include "cgal.h"
+#include "cgalutils.h"
 
 #ifdef ENABLE_CGAL
 
@@ -77,29 +78,24 @@ DxfData *CGAL_Nef_polyhedron::convertToDxfData() const
 	return dxfdata;
 }
 
-// dump the 2 dimensional nef_poly.
-std::string CGAL_Nef_polyhedron::dump_p2() const
+std::string CGAL_Nef_polyhedron::dump() const
 {
-        std::stringstream out;
-        CGAL_Nef_polyhedron2::Explorer explorer = this->p2->explorer();
-        CGAL_Nef_polyhedron2::Explorer::Vertex_const_iterator i;
-        out << "CGAL_Nef_polyhedron::p2 Vertices";
-        for (i = explorer.vertices_begin(); i != explorer.vertices_end(); ++i) {
-                if ( explorer.is_standard( i ) ) {
-                        CGAL_Nef_polyhedron2::Explorer::Point point = explorer.point( i );
-                        out << "\n Point x y: "
-                          << CGAL::to_double(point.x()) << " "
-                          << CGAL::to_double(point.y());
-                }  else {
-                        CGAL_Nef_polyhedron2::Explorer::Ray ray = explorer.ray( i );
-                        CGAL_Nef_polyhedron2::Explorer::Point point = ray.point( 0 );
-                        out << "\n Ray x y dx dy: "
-                          << CGAL::to_double(point.x()) << " " << CGAL::to_double(point.y()) << " "
-                          << CGAL::to_double(ray.direction().dx()) << " " << CGAL::to_double(ray.direction().dy());
-                }
-        }
-        out << "\nCGAL_Nef_polyhedron::p2 Vertices end";
-        return out.str();
+	if (this->dim==2)
+		return dump_cgal_nef_polyhedron2( *this->p2 );
+	else if (this->dim==3)
+		return dump_cgal_nef_polyhedron3( *this->p3 );
+	else
+		return std::string("Nef Polyhedron with dimension != 2 or 3");
+}
+
+std::string CGAL_Nef_polyhedron::dump_svg() const
+{
+	if (this->dim==2)
+		return dump_cgal_nef_polyhedron2_svg( *this->p2 );
+	else if (this->dim==3)
+		return dump_cgal_nef_polyhedron3_svg( *this->p3 );
+	else
+		return std::string("<svg><!--Nef Polyhedron with dimension != 2 or 3--></svg>");
 }
 
 #endif // ENABLE_CGAL
diff --git a/src/PolySetCGALEvaluator.cc b/src/PolySetCGALEvaluator.cc
index bca9902..19f5325 100644
--- a/src/PolySetCGALEvaluator.cc
+++ b/src/PolySetCGALEvaluator.cc
@@ -1,6 +1,7 @@
 #include "PolySetCGALEvaluator.h"
 #include "cgal.h"
 #include "cgalutils.h"
+#include <CGAL/convex_hull_3.h>
 #include "polyset.h"
 #include "CGALEvaluator.h"
 #include "projectionnode.h"
@@ -15,33 +16,23 @@
 #include "printutils.h"
 #include "openscad.h" // get_fragments_from_r()
 #include <boost/foreach.hpp>
+#include <vector>
 
-/*
-
-This Visitor is used in the 'cut' process. Essentially, one or more of
-our 3d nef polyhedrons have been 'cut' by the xy-plane, forming a number
-of polygons that are essentially 'flat'. This Visitor object, when
-called repeatedly, collects those flat polygons together and forms a new
-2d nef polyhedron out of them. It keeps track of the 'holes' so that
-in the final resulting polygon, they are preserved properly.
+typedef CGAL_Nef_polyhedron3::Point_3 Point_3;
 
-The output polygon is stored in the output_nefpoly2d variable.
+/*
 
-For more information on 3d + 2d nef polyhedrons, facets, halffacets,
-facet cycles, etc, please see these websites:
+This class converts multiple 3d-CGAL Nef polyhedrons into a single 2d by
+stripping off the z coordinate of each face vertex and doing unions and
+intersections. It uses the 'visitor' pattern from the CGAL manual.
+Output is in the 'output_nefpoly2d' variable.
 
+See also
 http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Nef_3/Chapter_main.html
-http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Nef_3_ref/Class_Nef_polyhedron_3-Traits---Halffacet.html
-
-The halffacet iteration 'circulator' code is based on OGL_helper.h
-
-Why do we throw out all 'down' half-facets? Imagine a triangle in 3d
-space - it has one 'half face' for one 'side' and another 'half face' for the
-other 'side'. If we iterated over both half-faces we would get the same vertex
-coordinates twice. Instead, we only need one side, in our case, we
-chose the 'up' side.
+http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Nef_3_ref/Class_Nef_polyhedron3.html
+OGL_helper.h
 */
-class NefShellVisitor_for_cut {
+class Flattener {
 public:
 	std::stringstream out;
 	CGAL_Nef_polyhedron2::Boundary boundary;
@@ -49,7 +40,7 @@ public:
 	shared_ptr<CGAL_Nef_polyhedron2> output_nefpoly2d;
 	CGAL::Direction_3<CGAL_Kernel3> up;
 	bool debug;
-	NefShellVisitor_for_cut(bool debug=false)
+	Flattener(bool debug=false)
 	{
 		output_nefpoly2d.reset( new CGAL_Nef_polyhedron2() );
 		boundary = CGAL_Nef_polyhedron2::INCLUDED;
@@ -67,11 +58,11 @@ public:
 	void visit( CGAL_Nef_polyhedron3::SFace_const_handle ) {}
 	void visit( CGAL_Nef_polyhedron3::Halffacet_const_handle hfacet ) {
 		if ( hfacet->plane().orthogonal_direction() != this->up ) {
-			if (debug) out << "down facing half-facet. skipping\n";
+			out << "\ndown facing half-facet. skipping\n";
 			return;
 		}
 
-		int numcontours = 0;
+		int contour_counter = 0;
 		CGAL_Nef_polyhedron3::Halffacet_cycle_const_iterator i;
 		CGAL_forall_facet_cycles_of( i, hfacet ) {
 			CGAL_Nef_polyhedron3::SHalfedge_around_facet_const_circulator c1(i), c2(c1);
@@ -82,14 +73,18 @@ public:
 				contour.push_back( point2d );
 			}
 			tmpnef2d.reset( new CGAL_Nef_polyhedron2( contour.begin(), contour.end(), boundary ) );
-			if ( numcontours == 0 ) {
-				if (debug) out << " contour is a body. make union(). " << contour.size() << " points.\n" ;
-				*output_nefpoly2d += *tmpnef2d;
+			if ( contour_counter == 0 ) {
+				if (debug) out << "\ncontour is a body. make union(). " << contour.size() << " points.\n" ;
+				*(output_nefpoly2d) += *(tmpnef2d);
 			} else {
-				if (debug) out << " contour is a hole. make intersection(). " << contour.size() << " points.\n";
-				*output_nefpoly2d *= *tmpnef2d;
+				*(output_nefpoly2d) *= *(tmpnef2d);
+				if (debug) out << "\ncontour is a hole. make intersection(). " << contour.size() << " points.\n";
 			}
-			numcontours++;
+      out << "\n------- tmp: -------\n";
+			if (debug) out << dump_cgal_nef_polyhedron2( *tmpnef2d );
+      out << "\n------- output accumulator: -------\n";
+			if (debug) out << dump_cgal_nef_polyhedron2( *output_nefpoly2d );
+			contour_counter++;
 		} // next facet cycle (i.e. next contour)
 	} // visit()
 };
@@ -120,39 +115,74 @@ PolySet *PolySetCGALEvaluator::evaluatePolySet(const ProjectionNode &node)
 		}
 	}
 
+	// std::cout << "----- input dump \n" << sum.dump_svg() << "\n";
+
 	CGAL_Nef_polyhedron nef_poly;
 
 	if (node.cut_mode) {
 		CGAL::Failure_behaviour old_behaviour = CGAL::set_error_behaviour(CGAL::THROW_EXCEPTION);
+		bool plane_intersect_fail = false;
 		try {
-			// intersect 'sum' with the x-y plane
 			CGAL_Nef_polyhedron3::Plane_3 xy_plane = CGAL_Nef_polyhedron3::Plane_3( 0,0,1,0 );
 			*sum.p3 = sum.p3->intersection( xy_plane, CGAL_Nef_polyhedron3::PLANE_ONLY);
-			
-			// Visit each polygon in sum.p3 and union/intersect into a 2d polygon (with holes)
-			// For info on Volumes, Shells, Facets, and the 'visitor' pattern, please see
-			// http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Nef_3/Chapter_main.html
-			NefShellVisitor_for_cut shell_visitor;
+		}
+		catch (const CGAL::Failure_exception &e) {
+			PRINTB("CGAL error in projection node during plane intersection: %s", e.what());
+			plane_intersect_fail = true;
+		}
+ 		if (plane_intersect_fail) {
+			try {
+				PRINT("Trying alternative intersection using very large thin box: ");
+			  double inf = 1e8, eps = 0.1;
+			  double x1 = -inf, x2 = +inf, y1 = -inf, y2 = +inf, z1 = 0, z2 = eps;
+
+				std::vector<Point_3> pts;
+				pts.push_back( Point_3( x1, y1, z1 ) );
+				pts.push_back( Point_3( x1, y2, z1 ) );
+				pts.push_back( Point_3( x2, y2, z1 ) );
+				pts.push_back( Point_3( x2, y1, z1 ) );
+				pts.push_back( Point_3( x1, y1, z2 ) );
+				pts.push_back( Point_3( x1, y2, z2 ) );
+				pts.push_back( Point_3( x2, y2, z2 ) );
+				pts.push_back( Point_3( x2, y1, z2 ) );
+
+				CGAL_Polyhedron bigbox;
+				CGAL::convex_hull_3( pts.begin(), pts.end(), bigbox );
+				CGAL_Nef_polyhedron3 nef_bigbox( bigbox );
+ 				*sum.p3 = nef_bigbox.intersection( *sum.p3 );
+			}
+			catch (const CGAL::Failure_exception &e) {
+				PRINTB("CGAL error in projection node during bigbox intersection: %s", e.what());
+				// fixme , can we just return empty polyset?
+				CGAL::set_error_behaviour(old_behaviour);
+				return NULL;
+			}
+		}
+
+		// remove z coordinates to make CGAL_Nef_polyhedron2
+		try {
+			Flattener flattener(true);
 			CGAL_Nef_polyhedron3::Volume_const_iterator i;
 			CGAL_Nef_polyhedron3::Shell_entry_const_iterator j;
 			CGAL_Nef_polyhedron3::SFace_const_handle sface_handle;
 			for ( i = sum.p3->volumes_begin(); i != sum.p3->volumes_end(); ++i ) {
 				for ( j = i->shells_begin(); j != i->shells_end(); ++j ) {
 					sface_handle = CGAL_Nef_polyhedron3::SFace_const_handle( j );
-					sum.p3->visit_shell_objects( sface_handle , shell_visitor );
+					sum.p3->visit_shell_objects( sface_handle , flattener );
 				}
 			}
-			if (debug) std::cout << "shell visitor\n" << shell_visitor.dump() << "\nshell visitor end\n";
-			
-			nef_poly.p2 = shell_visitor.output_nefpoly2d;
+
+			std::cout << "------- flattener dump \n" << flattener.dump() << "\n";
+			nef_poly.p2 = flattener.output_nefpoly2d;
 			nef_poly.dim = 2;
-			if (debug) std::cout << "--\n" << nef_poly.dump_p2() << "\n";
-		}
-		catch (const CGAL::Failure_exception &e) {
-			PRINTB("CGAL error in projection node: %s", e.what());
-			return NULL;
+		}	catch (const CGAL::Failure_exception &e) {
+			PRINTB("CGAL error in projection node while flattening: %s", e.what());
 		}
 
+		CGAL::set_error_behaviour(old_behaviour);
+
+		std::cout << "------- 3d cut dump \n" << sum.dump_svg() << "\n";
+		std::cout << "------- 2d output dump \n" << nef_poly.dump_svg() << "\n";
 		// Extract polygons in the XY plane, ignoring all other polygons
 		// FIXME: If the polyhedron is really thin, there might be unwanted polygons
 		// in the XY plane, causing the resulting 2D polygon to be self-intersection
diff --git a/src/cgal.h b/src/cgal.h
index e5e39dd..2ca82d3 100644
--- a/src/cgal.h
+++ b/src/cgal.h
@@ -54,6 +54,8 @@ typedef CGAL::Polyhedron_3<CGAL_Kernel3> CGAL_Polyhedron;
 typedef CGAL_Polyhedron::HalfedgeDS CGAL_HDS;
 typedef CGAL::Polyhedron_incremental_builder_3<CGAL_HDS> CGAL_Polybuilder;
 
+typedef CGAL::Cartesian<NT>::Iso_cuboid_3 CGAL_Iso_cuboid_3;
+
 #ifdef PREV_NDEBUG
 #define NDEBUG PREV_NDEBUG
 #endif
diff --git a/src/cgalutils.cc b/src/cgalutils.cc
index e402139..7ae6d7b 100644
--- a/src/cgalutils.cc
+++ b/src/cgalutils.cc
@@ -3,9 +3,11 @@
 #include "cgalutils.h"
 #include "polyset.h"
 #include "printutils.h"
-
 #include "cgal.h"
-
+#include <CGAL/bounding_box.h>
+typedef CGAL::Point_3<CGAL_Kernel3> CGAL_Point_3;
+typedef CGAL::Point_2<CGAL_Kernel2> CGAL_Point_2;
+#include <boost/algorithm/string.hpp>
 #include <map>
 
 PolySet *createPolySetFromPolyhedron(const CGAL_Polyhedron &p)
@@ -145,5 +147,296 @@ CGAL_Polyhedron *createPolyhedronFromPolySet(const PolySet &ps)
 	return P;
 }
 
+
+
+
+CGAL::Point project_svg3( CGAL_Point_3 p, CGAL_Iso_cuboid_3 bbox )
+{
+	// do extremely simple fake isometric projection, based on bounding box
+	double x = CGAL::to_double( p.x() );
+	double y = CGAL::to_double( p.y() );
+	double z = CGAL::to_double( p.z() );
+	double screenw = 480;
+	double screenh = 480;
+	double xcenter = screenw / 2;
+	double ycenter = screenh / 2;
+	double xdist = ( 2 * CGAL::to_double( bbox.xmax() - bbox.xmin() ) );
+	double ydist = ( 2 * CGAL::to_double( bbox.ymax() - bbox.ymin() ) );
+	double zdist = ( 2 * CGAL::to_double( bbox.zmax() - bbox.zmin() ) );
+	double xscale = (xdist==0) ? 1 : screenw / (xdist * 1.618);
+	double yscale = (ydist==0) ? 1 : screenh / (ydist * 1.618 * 3);
+	double zscale = (zdist==0) ? 1 : screenh / (zdist * 1.618);
+	double tx = xcenter + x * xscale + y * yscale;
+	double ty = ycenter - z * zscale - y * yscale;
+	return CGAL::Point( tx, ty, 0 );
+}
+
+CGAL::Point project_svg2( CGAL::Point p, CGAL_Iso_cuboid_3 bbox )
+{
+	CGAL_Point_3 pnew( p.x(), 0, p.y() );
+	return project_svg3( pnew, bbox );
+}
+
+// for debugging, not necessarily pretty or useful for users.
+std::string dump_cgal_nef_polyhedron2_face_svg(
+	CGAL_Nef_polyhedron2::Explorer::Halfedge_around_face_const_circulator c1,
+	CGAL_Nef_polyhedron2::Explorer::Halfedge_around_face_const_circulator c2,
+	CGAL_Nef_polyhedron2::Explorer explorer )
+{
+  std::stringstream out;
+	CGAL_For_all(c1, c2) {
+		if ( explorer.is_standard( explorer.target(c1) ) ) {
+			CGAL_Nef_polyhedron2::Explorer::Point source = explorer.point( explorer.source( c1 ) );
+			CGAL_Nef_polyhedron2::Explorer::Point target = explorer.point( explorer.target( c1 ) );
+			CGAL::Point tp1 = project_svg2( source );
+			CGAL::Point tp2 = project_svg2( target );
+      out << " <line"
+			  << " x1='" << CGAL::to_double(tp1.x()) << "'"
+			  << " x2='" << CGAL::to_double(tp1.y()) << "'"
+			  << " y1='" << CGAL::to_double(tp2.x()) << "'"
+			  << " y2='" << CGAL::to_double(tp2.y()) << "'"
+			  << " stroke='red' />\n";
+		}
+	}
+	return out.str();
+}
+
+std::string dump_cgal_nef_polyhedron2_svg( const CGAL_Nef_polyhedron2 &N )
+{
+  std::stringstream out;
+  CGAL_Nef_polyhedron2::Explorer explorer = N.explorer();
+  CGAL_Nef_polyhedron2::Explorer::Face_const_iterator i;
+  out << "<svg width='480px' height='480px' xmlns='http://www.w3.org/2000/svg' version='1.1'>\n";
+	out << "<polyline points='0,0 480,0 480,480 0,480' style='fill:none;stroke:black' />\n";
+	out << "<polyline points='10,455 10,475 10,465 18,465 2,465 10,465 14,461 6,469 10,465' style='fill:none;stroke:black;' />";
+	for ( i = explorer.faces_begin(); i!= explorer.faces_end(); ++i ) {
+			CGAL_Nef_polyhedron2::Explorer::Halfedge_around_face_const_circulator c1
+				= explorer.face_cycle( i ), c2 ( c1 );
+			out << dump_cgal_nef_polyhedron2_face_svg( c1, c2, explorer );
+
+/*
+	holes not implemented
+		  CGAL_Nef_polyhedron2::Explorer::Hole_const_iterator j;
+			for ( j = explorer.holes_begin( i ); j!= explorer.holes_end( i ); ++j ) {
+				CGAL_Nef_polyhedron2::Explorer::Halfedge_around_face_const_circulator c3( j ), c4 ( c3 );
+				out << dump_cgal_nef_polyhedron2_face_svg( c3, c4, explorer );
+			}
+*/
+  }
+  out << "</svg>";
+	std::string tmp = out.str();
+	boost::replace_all( tmp, "'", "\"" );
+	return tmp;
+}
+
+
+std::string dump_cgal_nef_polyhedron2_face(
+	CGAL_Nef_polyhedron2::Explorer::Halfedge_around_face_const_circulator c1,
+	CGAL_Nef_polyhedron2::Explorer::Halfedge_around_face_const_circulator c2,
+	CGAL_Nef_polyhedron2::Explorer explorer )
+{
+  std::stringstream out;
+	CGAL_For_all(c1, c2) {
+		out << "  On frame edge:" << explorer.is_frame_edge( c1 );
+		out << " Mark: " << explorer.mark( c1 );
+		if ( explorer.is_standard( explorer.target(c1) ) ) {
+			CGAL_Nef_polyhedron2::Explorer::Point source = explorer.point( explorer.source( c1 ) );
+			CGAL_Nef_polyhedron2::Explorer::Point target = explorer.point( explorer.target( c1 ) );
+      out  << "  Halfedge x y x2 y2: "
+				<< CGAL::to_double(source.x()) << " "
+				<< CGAL::to_double(source.y()) << " "
+				<< CGAL::to_double(target.x()) << " "
+				<< CGAL::to_double(target.y()) << "\n";
+		} else {
+			CGAL_Nef_polyhedron2::Explorer::Ray ray = explorer.ray( explorer.target( c1 ) );
+      out  << "  Ray x y dx dy: "
+				<< CGAL::to_double(ray.point(0).x()) << " "
+				<< CGAL::to_double(ray.point(0).y()) << " "
+				<< CGAL::to_double(ray.point(1).x()) << " "
+				<< CGAL::to_double(ray.point(1).y()) << "\n";
+		}
+	}
+	return out.str();
+}
+
+std::string dump_cgal_nef_polyhedron2( const CGAL_Nef_polyhedron2 &N )
+{
+  std::stringstream out;
+  CGAL_Nef_polyhedron2::Explorer explorer = N.explorer();
+  CGAL_Nef_polyhedron2::Explorer::Face_const_iterator i;
+  out << "CGAL_Nef_polyhedron2 dump begin\n";
+	for ( i = explorer.faces_begin(); i!= explorer.faces_end(); ++i ) {
+	    out << " Face body:\n";
+			CGAL_Nef_polyhedron2::Explorer::Halfedge_around_face_const_circulator c1
+				= explorer.face_cycle( i ), c2 ( c1 );
+			out << dump_cgal_nef_polyhedron2_face( c1, c2, explorer );
+
+		  CGAL_Nef_polyhedron2::Explorer::Hole_const_iterator j;
+			for ( j = explorer.holes_begin( i ); j!= explorer.holes_end( i ); ++j ) {
+		    out << "  Face hole:\n";
+				CGAL_Nef_polyhedron2::Explorer::Halfedge_around_face_const_circulator c3( j ), c4 ( c3 );
+				out << dump_cgal_nef_polyhedron2_face( c3, c4, explorer );
+			}
+  }
+  out << "CGAL_Nef_polyhedron2 dump end";
+  return out.str();
+}
+
+// This uses the Shell Explorer pattern from the CGAL Manual to dump the 3d Nef Polyhedron information
+// http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Nef_3/Chapter_main.html#Subsection_29.7.2
+class NefPoly3_dumper_svg {
+public:
+	std::stringstream out;
+	CGAL_Iso_cuboid_3 bbox;
+	NefPoly3_dumper_svg(const CGAL_Nef_polyhedron3& N) {}
+	void setbbox( CGAL_Iso_cuboid_3 bbox ) { this->bbox = bbox; }
+	void visit(CGAL_Nef_polyhedron3::Vertex_const_handle v) {}
+	void visit(CGAL_Nef_polyhedron3::Halfedge_const_handle ) {}
+	void visit(CGAL_Nef_polyhedron3::SHalfedge_const_handle ) {}
+	void visit(CGAL_Nef_polyhedron3::SHalfloop_const_handle shh ){}
+	void visit(CGAL_Nef_polyhedron3::SFace_const_handle ) {}
+	void visit( CGAL_Nef_polyhedron3::Halffacet_const_handle hfacet )
+	{
+		int contour_count = 0;
+		out << "  <!-- Halffacet. Mark: " << (*hfacet).mark() << " -->\n";
+		CGAL_Nef_polyhedron3::Halffacet_cycle_const_iterator i;
+		CGAL_forall_facet_cycles_of( i, hfacet ) {
+			CGAL_Nef_polyhedron3::SHalfloop_const_handle shl_handle;
+			out << "   <!-- Halffacet cycle: -->\n";
+			if ( contour_count == 0 ) {
+				out << "    <!-- Body contour:--> \n";
+			} else {
+				out << "    <!-- Hole contour:--> \n" ;
+			}
+			CGAL_Nef_polyhedron3::SHalfedge_around_facet_const_circulator c1(i), c2(c1);
+			CGAL_For_all( c1, c2 ) {
+				out << "     <line";
+				// don't know why we use source()->source(), except thats what CGAL does internally
+				CGAL_Point_3 source = c1->source()->source()->point();
+				CGAL_Point_3 target = c1->source()->target()->point();
+				tp1 = project_svg ( source );
+				tp2 = project_svg ( target );
+				out << " "
+					<< "x1='" << CGAL::to_double(tp1.x()) << "' "
+					<< "y1='" << CGAL::to_double(tp1.y()) << "' "
+					<< "x2='" << CGAL::to_double(tp2.x()) << "' "
+					<< "y2='" << CGAL::to_double(tp2.y()) << "' "
+				  << "stroke='red' />\n";
+			}
+			contour_count++;
+		} // next facet cycle (i.e. next contour)
+	} // visit()
+
+};
+
+
+std::string dump_cgal_nef_polyhedron3_svg( const CGAL_Nef_polyhedron3 &N )
+{
+  std::stringstream out;
+  out << "<svg width='480px' height='480px' xmlns='http://www.w3.org/2000/svg' version='1.1'>\n";
+	out << "<polyline points='0,0 480,0 480,480 0,480' style='fill:none;stroke:black' />\n";
+	out << "<polyline points='10,455 10,475 10,465 18,465 2,465 10,465 14,461 6,469 10,465' style='fill:none;stroke:black;' />";
+	out << "<!--CGAL_Nef_polyhedron3 dump begin-->\n";
+
+	std::vector<CGAL_Point_3> points;
+	CGAL_Nef_polyhedron3::Vertex_const_iterator vi;
+	for (vi = N.vertices_begin(); vi!=N.vertices_end(); ++vi)
+		points.push_back( vi->point() );
+	CGAL_Iso_cuboid_3 bbox = CGAL::bounding_box( points.begin(), points.end() );
+
+  CGAL_Nef_polyhedron3::Volume_const_iterator c;
+  CGAL_forall_volumes(c,N) {
+    out << " <!--Processing volume...-->\n";
+    out << "  <!--Mark: " << (*c).mark() << "-->\n";
+    CGAL_Nef_polyhedron3::Shell_entry_const_iterator it;
+    CGAL_forall_shells_of(it,c) {
+      out << "  <!--Processing shell...-->\n";
+      NefPoly3_dumper_svg dumper_svg(N);
+			dumper_svg.setbbox( bbox );
+      N.visit_shell_objects(CGAL_Nef_polyhedron3::SFace_const_handle(it), dumper_svg );
+			out << dumper_svg.out.str();
+      out << "  <!--Processing shell end-->\n";
+    }
+    out << " <!--Processing volume end-->\n";
+  }
+  out << "<!--CGAL_Nef_polyhedron3 dump end-->\n";
+	out << "</svg>";
+	std::string tmp = out.str();
+	boost::replace_all( tmp, "'", "\"" );
+  return tmp;
+}
+
+// This uses the Shell Explorer pattern from the CGAL Manual to dump the 3d Nef Polyhedron information
+// http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Nef_3/Chapter_main.html#Subsection_29.7.2
+class NefPoly3_dumper {
+public:
+	std::stringstream out;
+	NefPoly3_dumper(const CGAL_Nef_polyhedron3& N) {}
+	void visit(CGAL_Nef_polyhedron3::Vertex_const_handle v) {}
+	void visit(CGAL_Nef_polyhedron3::Halfedge_const_handle ) {}
+	void visit(CGAL_Nef_polyhedron3::SHalfedge_const_handle ) {}
+	void visit(CGAL_Nef_polyhedron3::SHalfloop_const_handle shh )
+	{
+		out << " SHalfloop visit\n";
+		out << "  Mark: " << (*shh).mark() << "\n";
+	}
+	void visit(CGAL_Nef_polyhedron3::SFace_const_handle ) {}
+	void visit( CGAL_Nef_polyhedron3::Halffacet_const_handle hfacet )
+	{
+		int contour_count = 0;
+		out << "  Halffacet visit\n";
+		out << "   Mark: " << (*hfacet).mark() << "\n";
+		CGAL_Nef_polyhedron3::Halffacet_cycle_const_iterator i;
+		CGAL_forall_facet_cycles_of( i, hfacet ) {
+			CGAL_Nef_polyhedron3::SHalfloop_const_handle shl_handle;
+			out << "   Halffacet cycle:\n";
+			if ( contour_count == 0 ) {
+				out << "    Body contour:\n";
+			} else {
+				out << "    Hole contour:\n" ;
+			}
+			CGAL_Nef_polyhedron3::SHalfedge_around_facet_const_circulator c1(i), c2(c1);
+			int count=0;
+			CGAL_For_all( c1, c2 ) {
+				out << "     Halfedge vertex:";
+				out << " Mark: " << (*c1).mark();
+				count++;
+				CGAL_Point_3 point3d = c1->source()->source()->point();
+				double x = CGAL::to_double( point3d.x() );
+				double y = CGAL::to_double( point3d.y() );
+		  	double z = CGAL::to_double( point3d.z() );
+			  out << " x:" << x << " y:" << y << " z:" << z <<"\n";
+			}
+	  		out << "     point count: " << count << "\n";
+			contour_count++;
+		} // next facet cycle (i.e. next contour)
+	} // visit()
+
+};
+
+std::string dump_cgal_nef_polyhedron3( const CGAL_Nef_polyhedron3 &N )
+{
+  std::stringstream out;
+  out << "CGAL_Nef_polyhedron3 dump begin\n";
+  CGAL_Nef_polyhedron3::Volume_const_iterator c;
+  CGAL_forall_volumes(c,N) {
+    out << " Processing volume...\n";
+    out << "  Mark: " << (*c).mark() << "\n";
+    CGAL_Nef_polyhedron3::Shell_entry_const_iterator it;
+    CGAL_forall_shells_of(it,c) {
+      out << "  Processing shell...\n";
+      NefPoly3_dumper dumper(N);
+      N.visit_shell_objects(CGAL_Nef_polyhedron3::SFace_const_handle(it), dumper );
+      out << dumper.out.str();
+      out << "  Processing shell end\n";
+    }
+    out << " Processing volume end\n";
+  }
+  out << "CGAL_Nef_polyhedron3 dump end\n";
+  return out.str();
+}
+
+
+
 #endif /* ENABLE_CGAL */
 
diff --git a/src/cgalutils.h b/src/cgalutils.h
index a249697..2bf6566 100644
--- a/src/cgalutils.h
+++ b/src/cgalutils.h
@@ -5,5 +5,9 @@
 
 class PolySet *createPolySetFromPolyhedron(const CGAL_Polyhedron &p);
 CGAL_Polyhedron *createPolyhedronFromPolySet(const class PolySet &ps);
+std::string dump_cgal_nef_polyhedron2( const CGAL_Nef_polyhedron2 &N );
+std::string dump_cgal_nef_polyhedron3( const CGAL_Nef_polyhedron3 &N );
+std::string dump_cgal_nef_polyhedron2_svg( const CGAL_Nef_polyhedron2 &N );
+std::string dump_cgal_nef_polyhedron3_svg( const CGAL_Nef_polyhedron3 &N );
 
 #endif