Some more checks and fixes in the IfcBooleanResult code. Most notably set the result to FirstOperand in case healing the result fails.

src/ifcgeom/IfcGeomFunctions.cpp

@@ -765,6 +765,8 @@ bool IfcGeom::Kernel::flatten_shape_list(const IfcGeom::IfcRepresentationShapeIt
 
 		if (shapes.size() == 1) {
 			result = moved_shape;
+			const double precision = getValue(GV_PRECISION);
+			apply_tolerance(result, precision);
 			return true;
 		}
 
@@ -791,7 +793,13 @@ bool IfcGeom::Kernel::flatten_shape_list(const IfcGeom::IfcRepresentationShapeIt
 		}
 	}
 
-	return !result.IsNull();
+	const bool success = !result.IsNull();
+	if (success) {
+		const double precision = getValue(GV_PRECISION);
+		apply_tolerance(result, precision);
+	}
+
+	return success;
 }
 	
 void IfcGeom::Kernel::remove_redundant_points_from_loop(TColgp_SequenceOfPnt& polygon, bool closed, double tol) {

src/ifcgeom/IfcGeomShapes.cpp

@@ -286,6 +286,8 @@ bool IfcGeom::Kernel::convert(const IfcSchema::IfcBooleanResult* l, TopoDS_Shape
 		if ( ! convert_shape(operand1, s1) ) {
 			return false;
 		}
+		{ TopoDS_Solid temp_solid;
+		s1 = ensure_fit_for_subtraction(s1, temp_solid); }
 	}
 
 	const double first_operand_volume = shape_volume(s1);
@@ -297,6 +299,10 @@ bool IfcGeom::Kernel::convert(const IfcSchema::IfcBooleanResult* l, TopoDS_Shape
 		shape2_processed = convert_shapes(operand2, items2) && flatten_shape_list(items2, s2, true);
 	} else {
 		shape2_processed = convert_shape(operand2,s2);
+		if (shape2_processed && !is_halfspace) {
+			TopoDS_Solid temp_solid;
+			s2 = ensure_fit_for_subtraction(s2, temp_solid);
+		}
 	}
 
 	if (!shape2_processed) {
@@ -321,8 +327,12 @@ bool IfcGeom::Kernel::convert(const IfcSchema::IfcBooleanResult* l, TopoDS_Shape
 			TopoDS_Shape result = brep_cut;
 
 			ShapeFix_Shape fix(result);
+			try {
 				fix.Perform();
 				result = fix.Shape();
+			} catch (...) {
+				Logger::Message(Logger::LOG_WARNING, "Shape healing failed on boolean result", l->entity);
+			}
 		
 			bool is_valid = BRepCheck_Analyzer(result).IsValid() != 0;
 			if ( is_valid ) {
@@ -355,10 +365,9 @@ bool IfcGeom::Kernel::convert(const IfcSchema::IfcBooleanResult* l, TopoDS_Shape
 			bool is_valid = BRepCheck_Analyzer(result).IsValid() != 0;
 			if ( is_valid ) {
 				shape = result;
-			} 
-		}
-
 				return true;
+			} 
+		}	
 
 	} else if (op == IfcSchema::IfcBooleanOperator::IfcBooleanOperator_INTERSECTION) {
 
@@ -373,16 +382,14 @@ bool IfcGeom::Kernel::convert(const IfcSchema::IfcBooleanResult* l, TopoDS_Shape
 			bool is_valid = BRepCheck_Analyzer(result).IsValid() != 0;
 			if ( is_valid ) {
 				shape = result;
-			} 
-		}
-
 				return true;
-
-	} else {
-		return false;
 			} 
 		}
 
+	}
+	return false;
+}
+
 bool IfcGeom::Kernel::convert(const IfcSchema::IfcConnectedFaceSet* l, TopoDS_Shape& shape) {
 	IfcSchema::IfcFace::list::ptr faces = l->CfsFaces();
 	bool facesAdded = false;