Use the precision from the IfcGeometricRepresentationContext to dictate OCC modeler tolerances

src/ifcgeom/IfcGeom.h

@@ -73,6 +73,10 @@ namespace IfcGeom {
 		// the interpretation of IfcParamaterValues of IfcTrimmedCurves
 		// Default: -1.0 (= not set, fist try degrees, then radians)
 		GV_PLANEANGLE_UNIT,
+		// The precision used in boolean operations, setting this value too low results
+		// in artefacts and potentially modelling failures
+		// Default: 0.00001 (obtained from IfcGeometricRepresentationContext if available)
+		GV_PRECISION
 	};
 
 	bool convert_wire_to_face(const TopoDS_Wire& wire, TopoDS_Face& face);
@@ -95,6 +99,7 @@ namespace IfcGeom {
 	bool profile_helper(int numVerts, double* verts, int numFillets, int* filletIndices, double* filletRadii, gp_Trsf2d trsf, TopoDS_Face& face); 
 	double shape_volume(const TopoDS_Shape& s);
 	double face_area(const TopoDS_Face& f);
+	void apply_tolerance(TopoDS_Shape& s, double t);
 	void SetValue(GeomValue var, double value);
 	double GetValue(GeomValue var);
 	Ifc2x3::IfcProductDefinitionShape* tesselate(TopoDS_Shape& shape, double deflection, IfcEntities es);

src/ifcgeom/IfcGeomFunctions.cpp

@@ -423,6 +423,11 @@ gp_Pnt IfcGeom::point_above_plane(const gp_Pln& pln, bool agree) {
 	}
 }
 
+void IfcGeom::apply_tolerance(TopoDS_Shape& s, double t) {
+	ShapeFix_ShapeTolerance tol;
+	tol.SetTolerance(s, t);
+}
+
 static double deflection_tolerance = 0.001;
 static double wire_creation_tolerance = 0.0001;
 static double minimal_face_area = 0.000001;
@@ -431,6 +436,7 @@ static double max_faces_to_sew = -1.0;
 static double ifc_length_unit = 1.0;
 static double ifc_planeangle_unit = -1.0;
 static double force_ccw_face_orientation = -1.0;
+static double modelling_precision = 0.00001;
 
 void IfcGeom::SetValue(GeomValue var, double value) {
 	switch (var) {
@@ -458,6 +464,9 @@ void IfcGeom::SetValue(GeomValue var, double value) {
 	case GV_FORCE_CCW_FACE_ORIENTATION:
 		force_ccw_face_orientation = value;
 		break;
+	case GV_PRECISION:
+		modelling_precision = value;
+		break;
 	default:
 		assert(!"never reach here");
 	}
@@ -484,6 +493,9 @@ double IfcGeom::GetValue(GeomValue var) {
 	case GV_FORCE_CCW_FACE_ORIENTATION:
 		return force_ccw_face_orientation;
 		break;
+	case GV_PRECISION:
+		return modelling_precision;
+		break;
 	}
 	assert(!"never reach here");
 	return 0;

src/ifcgeom/IfcGeomObjects.cpp

@@ -573,6 +573,32 @@ double UnitPrefixToValue( Ifc2x3::IfcSIPrefix::IfcSIPrefix v ) {
 	else return 1.0f;
 }
 
+void IfcGeomObjects::InitPrecision() {
+	Ifc2x3::IfcGeometricRepresentationContext::list rep_contexts = ifc_file->EntitiesByType<Ifc2x3::IfcGeometricRepresentationContext>();
+	// Currently, IfcGeometricRepresentationContext aren't used as much as they should be
+	// in the evaluation of shape representations, hence, we try to find the one with the
+	// lowest precision. Typically, a value of 1e-5 is encountered. This value is applied
+	// to all TopoDS_Shapes generated by one of the IfcGeom::convert() functions.
+	// TODO: Many of the empirically found tolerances should probably be substituted by
+	// one that is defined in the model file.
+	double lowest_precision_encountered = std::numeric_limits<double>::infinity();
+	bool any_precision_encountered = false;
+	for (Ifc2x3::IfcGeometricRepresentationContext::it it = rep_contexts->begin(); it != rep_contexts->end(); ++it) {
+		Ifc2x3::IfcGeometricRepresentationContext* rep_context = *it;
+		if (rep_context->is(Ifc2x3::Type::IfcGeometricRepresentationSubContext)) continue;
+		if (rep_context->hasPrecision()) {
+			const double precision = rep_context->Precision();
+			if (precision < lowest_precision_encountered) {
+				any_precision_encountered = true;
+				lowest_precision_encountered = precision;
+			}
+		}
+	}
+	if (any_precision_encountered) {
+		IfcGeom::SetValue(IfcGeom::GV_PRECISION, lowest_precision_encountered);
+	}
+}
+
 void IfcGeomObjects::InitUnits() {
 	// Set default units, set length to meters, angles to undefined
 	IfcGeom::SetValue(IfcGeom::GV_LENGTH_UNIT,1.0);
@@ -638,6 +664,7 @@ bool IfcGeomObjects::Init(const std::string fn) {
 }
 bool _Init() {
 	IfcGeomObjects::InitUnits();
+	IfcGeomObjects::InitPrecision();
 
 	shapereps = ifc_file->EntitiesByType<Ifc2x3::IfcShapeRepresentation>();
 	if ( ! shapereps ) return false;

src/ifcgeom/IfcGeomObjects.h

@@ -265,6 +265,7 @@ namespace IfcGeomObjects {
 	
 	void Settings(int setting, bool value);
 	void InitUnits();
+	void InitPrecision();
 	
 	const IfcGeomObject* Get();
 	const IfcObject* GetObject(int id);

src/ifcgeom/IfcGeomShapes.cpp

@@ -158,19 +158,6 @@ bool IfcGeom::convert(const Ifc2x3::IfcBooleanClippingResult::ptr l, TopoDS_Shap
 	Ifc2x3::IfcBooleanOperand operand1 = l->FirstOperand();
 	Ifc2x3::IfcBooleanOperand operand2 = l->SecondOperand();
 	bool is_halfspace = operand2->is(Ifc2x3::Type::IfcHalfSpaceSolid);
-	bool is_bounded = operand2->is(Ifc2x3::Type::IfcPolygonalBoundedHalfSpace);
-
-	// The rationale of this elaborate processing of bounded halfspace subtractions
-	// is that occasionally we have encountered bounded halfspaces of which the
-	// boundary coincides roughly with the footprint of the first operand solid and
-	// subtracting this naively resulted in precision artefacts. However, when the
-	// final subtraction result is the outcome of multiple successive bounded 
-	// halfspace subtractions the added complexity of this scheme can potentially
-	// produce wrong results too. Hence this check.
-	bool parent_is_bounded_halfspace = operand1->is(Ifc2x3::Type::IfcBooleanClippingResult) &&
-		((Ifc2x3::IfcBooleanClippingResult*) operand1)->SecondOperand()->is(Ifc2x3::Type::IfcPolygonalBoundedHalfSpace);
-
-	bool is_convex_bound = false;
 
 	if ( ! IfcGeom::convert_shape(operand1,s1) )
 		return false;
@@ -185,13 +172,6 @@ bool IfcGeom::convert(const Ifc2x3::IfcBooleanClippingResult::ptr l, TopoDS_Shap
 		return true;
 	}
 
-	if ( is_bounded ) {
-		Ifc2x3::IfcPolygonalBoundedHalfSpace::ptr ifc_bounded_halfspace = 
-			(Ifc2x3::IfcPolygonalBoundedHalfSpace::ptr) operand2;		
-		IfcGeom::convert_wire(ifc_bounded_halfspace->PolygonalBoundary(),boundary_wire);
-		is_convex_bound = is_convex(boundary_wire);
-	}
-
 	if ( ! is_halfspace ) {
 		const double second_operand_volume = shape_volume(s2);
 		if ( second_operand_volume <= ALMOST_ZERO )
@@ -199,102 +179,19 @@ bool IfcGeom::convert(const Ifc2x3::IfcBooleanClippingResult::ptr l, TopoDS_Shap
 	}
 
 	bool valid_cut = false;
-	if ( !is_bounded || !is_convex_bound || parent_is_bounded_halfspace) {
-		BRepAlgoAPI_Cut brep_cut(s1,s2);
-		if ( brep_cut.IsDone() ) {
-			TopoDS_Shape result = brep_cut;
-			bool is_valid = BRepCheck_Analyzer(result).IsValid() != 0;
-			if ( is_valid ) {
-				shape = result;
-				valid_cut = true;
-			} 
-		}
-		if ( !valid_cut && !is_bounded ) {
-			Ifc2x3::IfcHalfSpaceSolid::ptr ifc_halfspace = (Ifc2x3::IfcHalfSpaceSolid::ptr) operand2;
-			Ifc2x3::IfcSurface::ptr surface = ifc_halfspace->BaseSurface();
-			if ( surface->is(Ifc2x3::Type::IfcPlane) ) {
-				gp_Pln pln;
-				IfcGeom::convert(reinterpret_pointer_cast<Ifc2x3::IfcSurface,Ifc2x3::IfcPlane>(surface),pln);
-				gp_Pnt pnt = pln.Location();
-				bool reverse = ifc_halfspace->AgreementFlag();
-				gp_Vec direction = pln.Axis().Direction();
-				if ( reverse ) direction *= -1;
-				pnt.Translate(direction);
-				pln.SetLocation(pln.Location().Translated(direction * -0.0001));
-				TopoDS_Shape halfspace = BRepPrimAPI_MakeHalfSpace(BRepBuilderAPI_MakeFace(pln),pnt).Solid();
+	BRepAlgoAPI_Cut brep_cut(s1,s2);
+	if ( brep_cut.IsDone() ) {
+		TopoDS_Shape result = brep_cut;
 
-				BRepAlgoAPI_Cut brep_cut(s1,halfspace);
-				if ( brep_cut.IsDone() ) {
-					TopoDS_Shape result = brep_cut;
-					bool is_valid = BRepCheck_Analyzer(result).IsValid() != 0;
-					if ( is_valid ) {
-						shape = result;
-						valid_cut = true;
-						Logger::Message(Logger::LOG_WARNING,"Slightly nudged the SecondOperand of:",l->entity);
-					} 
-				}
-			}
-		}
-	} else {
-		Ifc2x3::IfcPolygonalBoundedHalfSpace::ptr ifc_bounded_halfspace = 
-			(Ifc2x3::IfcPolygonalBoundedHalfSpace::ptr) operand2;
-		gp_Trsf trsf;
-		convert(ifc_bounded_halfspace->Position(),trsf);
-		TopoDS_Shape face = BRepBuilderAPI_MakeFace(boundary_wire).Face();
-		TopoDS_Shape prism = BRepPrimAPI_MakePrism (boundary_wire,gp_Vec(0,0,1),1);
-		prism.Move(trsf);
-		face.Move(trsf);
-
-		gp_Pln pln = plane_from_face(TopoDS::Face(face));
-		gp_Pnt pnt = point_above_plane(pln,ifc_bounded_halfspace->AgreementFlag());
-
-		TopoDS_Shape halfspace;
-		Ifc2x3::IfcHalfSpaceSolid::ptr ifc_halfspace = (Ifc2x3::IfcHalfSpaceSolid::ptr) operand2;
-		if ( ! IfcGeom::convert(ifc_halfspace,halfspace) ) return false;
-
-		TopoDS_Shape subtraction_volume = s1;
-		double subtraction_volume_volume = shape_volume(subtraction_volume);
-
-		const double minimal_substraction_difference = subtraction_volume_volume * 0.0001;
-
-		BRepAlgoAPI_Common brep_common(subtraction_volume,halfspace);
-		if ( brep_common.IsDone() ) {
-			TopoDS_Shape brep_common_shape = brep_common;
-			bool is_valid = BRepCheck_Analyzer(brep_common_shape).IsValid() != 0;
-			double new_subtraction_volume_volume = shape_volume(brep_common_shape);
-			double subtraction_volume_difference = subtraction_volume_volume - new_subtraction_volume_volume;
-			if ( is_valid && subtraction_volume_difference > minimal_substraction_difference ) {
-				subtraction_volume = brep_common_shape;
-				subtraction_volume_volume = new_subtraction_volume_volume;
-			}
-		}
-
-		TopExp_Explorer exp(prism,TopAbs_FACE);
-		while ( exp.More() ) {
-			TopoDS_Shape halfspace = halfspace_from_plane(plane_from_face(TopoDS::Face(exp.Current())),pnt);
-			BRepAlgoAPI_Common brep_common(subtraction_volume,halfspace);
-			if ( brep_common.IsDone() ) {
-				TopoDS_Shape brep_common_shape = brep_common;
-				bool is_valid = BRepCheck_Analyzer(brep_common_shape).IsValid() != 0;
-				double new_subtraction_volume_volume = shape_volume(brep_common_shape);
-				double subtraction_volume_difference = subtraction_volume_volume - new_subtraction_volume_volume;
-				if ( is_valid && subtraction_volume_difference > minimal_substraction_difference ) {
-					subtraction_volume = brep_common_shape;
-					subtraction_volume_volume = new_subtraction_volume_volume;
-				}
-			}
-			exp.Next();
-		}
-
-		BRepAlgoAPI_Cut brep_cut(s1,subtraction_volume);
-		if ( brep_cut.IsDone() ) {
-			TopoDS_Shape result = brep_cut;
-			bool is_valid = BRepCheck_Analyzer(result).IsValid() != 0;
-			if ( is_valid ) {
-				shape = result;
-				valid_cut = true;
-			} 
-		}
+		ShapeFix_Shape fix(result);
+		fix.Perform();
+		result = fix.Shape();
+		
+		bool is_valid = BRepCheck_Analyzer(result).IsValid() != 0;
+		if ( is_valid ) {
+			shape = result;
+			valid_cut = true;
+		} 
 	}
 
 	if ( valid_cut ) {
@@ -307,7 +204,6 @@ bool IfcGeom::convert(const Ifc2x3::IfcBooleanClippingResult::ptr l, TopoDS_Shap
 	}
 
 	return true;
-
 }
 bool IfcGeom::convert(const Ifc2x3::IfcConnectedFaceSet::ptr l, TopoDS_Shape& shape) {
 	Ifc2x3::IfcFace::list faces = l->CfsFaces();

src/ifcgeom/IfcRegister.cpp

@@ -42,11 +42,19 @@ bool IfcGeom::is_shape_collection(const IfcBaseClass* l) {
 }
 bool IfcGeom::convert_shape(const IfcBaseClass* l, TopoDS_Shape& r) {
 	const unsigned int id = l->entity->id();
+	bool success = false;
+	bool processed = false;
 	std::map<int,TopoDS_Shape>::const_iterator it = Cache::Shape.find(id);
 	if ( it != Cache::Shape.end() ) { r = it->second; return true; }
 #include "IfcRegisterConvertShape.h"
-	Logger::Message(Logger::LOG_ERROR,"No operation defined for:",l->entity);
-	return 0;
+	if ( processed ) { 
+		const double precision = IfcGeom::GetValue(GV_PRECISION);
+		IfcGeom::apply_tolerance(r, precision);
+		Cache::Shape[id] = r;
+	} else {
+		Logger::Message(Logger::LOG_ERROR,"No operation defined for:",l->entity);
+	}
+	return success;
 }
 bool IfcGeom::convert_wire(const IfcBaseClass* l, TopoDS_Wire& r) {
 #include "IfcRegisterConvertWire.h"

src/ifcgeom/IfcRegisterConvertShape.h

@@ -1,14 +1,16 @@
 #include "IfcRegisterUndef.h"
 #define SHAPE(T) \
-	if ( l->is(T::Class()) ) { \
+	if ( !processed && l->is(T::Class()) ) { \
+		processed = true; \
 		try { \
 			if ( convert((T*)l,r) ) { \
-				Cache::Shape[id] = r; \
-				return true; \
+				success = true; \
 			} \
 		} catch(...) {  } \
-		Logger::Message(Logger::LOG_ERROR,"Failed to convert:",l->entity); \
-		return 0; \
+		if ( !success) { \
+			Logger::Message(Logger::LOG_ERROR,"Failed to convert:",l->entity); \
+			return false; \
+		} \
 	}
 #include "IfcRegisterDef.h"