|Boundary Representation - NURBS|
|Représentation frontière avancée|
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.
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
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
|HasAdvancedFaces||Each face of the advanced B-rep shall be of type IfcAdvancedFace.|
|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.
|IfcDimensionCount||The space dimensionality of this class, it is always 3.||X|
|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.||X|