IFC 4.3.x development IfcShellBasedSurfaceModel Semantic definitions at the entity

An IfcShellBasedSurfaceModel represents the shape by a set of open or closed shells. The connected faces within the shell have a dimensionality 2 and are placed in a coordinate space of dimensionality 3.

NOTE  Definition according to ISO/CD 10303-42:1992
A shell based surface model is described by a set of open or closed shells of dimensionality 2. The shells shall not intersect except at edges and vertices. In particular, distinct faces may not intersect. A complete face of one shell may be shared with another shell. Coincident portions of shells shall both reference the same faces, edges and vertices defining the coincident region. There shall be at least one shell. A shell may exist independently of a surface model.

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

HISTORY  New entity in IFC2x.

Informal Propositions:

  1. The dimensionality of the shell based surface model is 2.
  2. The shells shall not overlap or intersect except at common faces, edges or vertices. Attributes

# Attribute Type Description
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.
1 SbsmBoundary SET [1:?] OF IfcShell
Dim INVALID The space dimensionality of this class, it is always 3. Entity inheritance

dot_inheritance IfcShellBasedSurfaceModel IfcShellBasedSurfaceModel IfcGeometricRepresentationItem IfcGeometricRepresentationItem IfcShellBasedSurfaceModel->IfcGeometricRepresentationItem IfcGeometricRepresentationItem_children 24 more... IfcGeometricRepresentationItem_children->IfcGeometricRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcGeometricRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem Formal representations

ENTITY IfcShellBasedSurfaceModel
 SUBTYPE OF (IfcGeometricRepresentationItem);
	SbsmBoundary : SET [1:?] OF IfcShell;
	 Dim : IfcDimensionCount := 3;