mark bounds as external based on entity type

src/ifcgeom/schema/mapping.cpp

@@ -176,6 +176,13 @@ taxonomy::item* mapping::map_impl(const IfcSchema::IfcFace* inst) {
 			if (!bound->Orientation()) {
 				r->reverse();
 			}
+			if (bound->declaration().is(IfcSchema::IfcFaceOuterBound::Class())) {
+				// Make a copy in case we need immutability later for e.g. caching
+				auto s = r->clone();
+				((taxonomy::loop*)s)->external = true;
+				delete r;
+				r = s;
+			}
 			face->children.push_back(r);
 		}		
 	}