8.8.3.1 IfcAdvancedBrep

8.8.3.1.1 Semantic definition

An advanced B-rep is a boundary representation model in which all faces, edges and vertices are explicitly represented. It is a solid with explicit topology and elementary or free-form geometry. The faces of the B-rep are of type IfcAdvancedFace. An advanced B-rep has to meet the same topological constraints as the manifold solid B-rep.

advanced brep b-spline surface — Figure A — Advanced Brep, b-spline surface

Figure A illustrates use of IfcAdvancedBrep for boundary representation models with b-spline surfaces. The diagram shows the topological and geometric representation items that are used for advanced B-reps, based on IfcAdvancedFace.

advanced brep elementary surface — Figure B — Advanced Brep, elementary surface

Figure B illustrates use of IfcAdvancedBrep for boundary representation models with elementary surfaces. The diagram shows the topological and geometric representation items that are used for advanced B-reps, based on IfcAdvancedFace. It shows the use of IfcIntersectionCurve to provide the geometric representation of the edge curve both as 3D curve and as u,v pcurve in the parametric space of the adjacent surfaces.

Informal Propositions

each face is a face surface;
each face surface has its geometry defined by an elementary surface, swept surface or a b-spline surface;
the edges used to define the boundaries of the face shall all reference an edge curve
each curve used to define the geometry of the faces and face bounds shall be either a conic, or a line or a polyline or a b-spline curve
the edges used to define the face boundaries shall all be trimmed by vertices of type vertex point
no loop used to define a face bound shall be of the oriented subtype

8.8.3.1.2 Entity inheritance

8.8.3.1.3 Attributes

#	Attribute	Type	Description
IfcRepresentationItem (2)
	LayerAssignment	SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems	Assignment of the representation item to a single or multiple layer(s). The LayerAssignments can override a LayerAssignments of the IfcRepresentation it is used within the list of Items. IFC2x3-CHANGE The inverse attribute LayerAssignments has been added. IFC4-CHANGE The inverse attribute LayerAssignment has been restricted to max 1. Upward compatibility for file based exchange is guaranteed.
	StyledByItem	SET [0:1] OF IfcStyledItem FOR Item	Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve. IFC2x3-CHANGE The inverse attribute StyledByItem has been added.
IfcSolidModel (1)
*	Dim	IfcDimensionCount	This attribute is formally derived. `3` The space dimensionality of this class, it is always 3.
Click to show 3 hidden inherited attributes Click to hide 3 inherited attributes
IfcManifoldSolidBrep (1)
1	Outer	IfcClosedShell	A closed shell defining the exterior boundary of the solid. The shell normal shall point away from the interior of the solid.

Table C

8.8.3.1.4 Formal propositions

Name	Description
HasAdvancedFaces	Each face of the advanced B-rep shall be of type IfcAdvancedFace.
`SIZEOF(QUERY(Afs <* SELF\IfcManifoldSolidBrep.Outer.CfsFaces \| (NOT ('IFC4X4_DEV_20260525.IFCADVANCEDFACE' IN TYPEOF(Afs))) )) = 0`

Table D

8.8.3.1.5 Formal representation

ENTITY IfcAdvancedBrep
SUPERTYPE OF (ONEOF
(IfcAdvancedBrepWithVoids))
SUBTYPE OF (IfcManifoldSolidBrep);
WHERE
HasAdvancedFaces : SIZEOF(QUERY(Afs <* SELF\IfcManifoldSolidBrep.Outer.CfsFaces |
(NOT ('IFC4X4_DEV_20260525.IFCADVANCEDFACE' IN TYPEOF(Afs)))
)) = 0;
END_ENTITY;