IFC 4.3.x development

8.8.3.16 IfcFaceBasedSurfaceModel

8.8.3.16.1 Semantic definitions at the entity

The IfcFaceBasedSurfaceModel represents the a shape by connected face sets. The connected faces have a dimensionality 2 and are placed in a coordinate space of dimensionality 3.

NOTE  Definition according to ISO/CD 10303-42:1992
A face based surface model is described by a set of connected face sets of dimensionality 2. The connected face sets shall not intersect except at edges and vertices, except that a face in one connected face set may overlap a face in another connected face set, provided the face boundaries are identical. There shall be at least one connected face set.
A connected face set may exist independently of a surface model.

NOTE  Entity adapted from face_based_surface_model defined in ISO 10303-42.

HISTORY  New entity in IFC2x.

Informal Propositions:

  1. The connected face sets shall not overlap or intersect except at common faces, edges or vertices.
  2. The fbsm faces have dimensionality 2.

IFC4 CHANGE  The entity has been deprecated and shall not be used. The entity IfcFacetedBrep shall be used instead.

8.8.3.16.1 Attributes

# Attribute Type Description
IfcRepresentationItem
LayerAssignmentSET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItemsAssignment 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.
IfcGeometricRepresentationItem
IfcFaceBasedSurfaceModel
1 FbsmFaces SET [1:?] OF IfcConnectedFaceSet The set of connected face sets comprising the face based surface model.
Dim INVALID The space dimensionality of this class, it is always 3.

8.8.3.16.2 Entity inheritance

dot_inheritance IfcFaceBasedSurfaceModel IfcFaceBasedSurfaceModel IfcGeometricRepresentationItem IfcGeometricRepresentationItem IfcFaceBasedSurfaceModel->IfcGeometricRepresentationItem IfcGeometricRepresentationItem_children 24 more... IfcGeometricRepresentationItem_children->IfcGeometricRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcGeometricRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem

8.8.3.16.3 Formal representations

ENTITY IfcFaceBasedSurfaceModel
 SUBTYPE OF (IfcGeometricRepresentationItem);
	FbsmFaces : SET [1:?] OF IfcConnectedFaceSet;
 DERIVE
	 Dim : IfcDimensionCount := 3;
END_ENTITY;