Natural language names
Boundary Representation - NURBS
Advanced Brep
Représentation frontière avancée
Change log
Semantic definitions at the entity
Entity 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.

NOTE  The advanced B-rep has been introduced in order to support the increasing number of applications that can define and exchange B-rep models based on NURBS or other b-spline surfaces.
advanced brep b-spline surface

Figure 347 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.

Figure 347 — Advanced Brep, b-spline surface


   advanced brep elementary surface

Figure 348 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.

Figure 348 — Advanced Brep, elementary surface

NOTE  Entity adapted from advanced_brep_shape_representation defined in ISO 10303-514.
HISTORY  New entity in IFC4

Informal Propositions:

  1. each face is a face surface;
  2. each face surface has its geometry defined by an elementary surface, swept surface or a b-spline surface;
  3. the edges used to define the boundaries of the face shall all reference an edge curve
  4. 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
  5. the edges used to define the face boundaries shall all be trimmed by vertices of type vertex point
  6. no loop used to define a face bound shall be of the oriented subtype
Formal Propositions
HasAdvancedFacesEach face of the advanced B-rep shall be of type IfcAdvancedFace.
Inherited definitions from supertypes
Entity inheritance IfcAdvancedBrepWithVoids IfcManifoldSolidBrep IfcSolidModel IfcGeometricRepresentationItem IfcRepresentationItem
Attribute inheritance
S[0:1]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.
S[0:1]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.
IfcDimensionCountThe space dimensionality of this class, it is always 3. X
1OuterIfcClosedShell A closed shell defining the exterior boundary of the solid. The shell normal shall point away from the interior of the solid.X
Formal representations
XML Specification
 <xs:element name="IfcAdvancedBrep" type="ifc:IfcAdvancedBrep" substitutionGroup="ifc:IfcManifoldSolidBrep" nillable="true"/>
 <xs:complexType name="IfcAdvancedBrep">
   <xs:extension base="ifc:IfcManifoldSolidBrep"/>
EXPRESS Specification
ENTITY IfcAdvancedBrep
 SUPERTYPE OF(IfcAdvancedBrepWithVoids)
 SUBTYPE OF (IfcManifoldSolidBrep);
  HasAdvancedFaces : SIZEOF(QUERY(Afs <* SELF\IfcManifoldSolidBrep.Outer.CfsFaces |
)) = 0;

Link to EXPRESS-G diagram EXPRESS-G diagram

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