## 8.20.3.1.1 Semantic definition

An advanced face is a specialization of a face surface that has to meet requirements on using particular topological and geometric representation items for the definition of the faces, edges and vertices.

In case of closed faces with periodic surfaces, such as cylindrical or spherical surfaces, the following applies:

• the edges of the closed surface, in case of a cylindrical surface the upper and lower cap, refer to the same instance of IfcVertexPoint twice,
• no IfcFaceOuterBound is provided, or the IfcFaceOuterBound is constructed using an IfcSeamCurve at the periodic end of the underlying closed surface, in case of a cylindrical surface at 0./360. degree.

## 8.20.3.1.5 Formal representation

ENTITY IfcAdvancedFace
SUBTYPE OF (IfcFaceSurface);
WHERE
ApplicableEdgeCurves : SIZEOF(QUERY (ElpFbnds <*
QUERY (Bnds <* SELF\IfcFace.Bounds |
NOT (SIZEOF (QUERY (Oe <* ElpFbnds.Bound\IfcEdgeLoop.EdgeList |
TYPEOF(Oe\IfcOrientedEdge.EdgeElement\IfcEdgeCurve.EdgeGeometry)) = 1 )
)) = 0
))) = 0;
ApplicableSurface : SIZEOF (
TYPEOF(SELF\IfcFaceSurface.FaceSurface)) = 1;
RequiresEdgeCurve : SIZEOF(QUERY (ElpFbnds <*
QUERY (Bnds <* SELF\IfcFace.Bounds |
NOT (SIZEOF (QUERY (Oe <* ElpFbnds.Bound\IfcEdgeLoop.EdgeList |
END_ENTITY;