IfcShapeRepresentation

Semantic definitions at the entity

Entity definition

Definition from ISO/CD 10303-42:1992: The shape representation is a specific kind of representation that represents a shape.

Definition from IAI: The IfcShapeRepresentation represents the concept of a particular geometric representation of a product or a product component within a specific geometric representation context. The inherited attribute RepresentationType is used to define the geometric model used for the shape representation, the inherited attribute RepresentationIdentifier is used to denote the part of the representation captured by the IfcShapeRepresentation (e.g. Axis, Body, etc.).

Several representation types for shape representation are included as predefined types:

Curve2D		2 dimensional curves
GeometricSet		points, curves, surfaces (2 or 3 dimensional)
	GeometricCurveSet	points, curves (2 or 3 dimensional)
	Annotation2D	points, curves (2 or 3 dimensional), hatches and text (2 dimensional)
SurfaceModel		face based and shell based surface model
SolidModel		including swept solid, Boolean results and Brep bodies more specific types are:
	SweptSolid	swept area solids, by extrusion and revolution
	Brep	faceted Brep's with and without voids
	CSG	Boolean results of operations between solid models, half spaces and Boolean results
	Clipping	Boolean differences between swept area solids, half spaces and Boolean results
	AdvancedSweptSolid	swept area solids created by sweeping a profile along a directrix
additional types		some additional representation types are given:
	BoundingBox	simplistic 3D representation by a bounding box
	SectionedSpine	cross section based representation of a spine curve and planar cross sections. It can represent a surface or a solid and the interpolations of the between the cross sections is not defined
	MappedRepresentation	representation based on mapped item(s), referring to a representation map. Note: it can be seen as an inserted block reference. The shape representation of the mapped item has a representation type declaring the type of its representation items.

Table 1: string values for the inherited attribute 'RepresentationType'.

NOTE The definition of this entity relates to the STEP entity shape_representation. Please refer to ISO/IS 10303-41:1994 for the final definition of the formal standard.

HISTORY New entity in IFC Release 1.5.

Formal Propositions

Rule	Description
WR21	The context to which the IfcShapeRepresentation is assign, shall be of type IfcGeometricRepresentationContext.
WR22	No topological representation item shall be directly used for shape representations, with the exception of IfcVertexPoint, IfcEdgeCurve, IfcFaceSurface.
WR23	A representation type should be given to the shape representation.
WR24	Checks the proper use of Items according to the RepresentationType.

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	A
IfcRepresentation
1	ContextOfItems	IfcRepresentationContext	[1:1]	Definition of the representation context for which the different subtypes of representation are valid.	X
2	RepresentationIdentifier	IfcLabel	[0:1]	The optional identifier of the representation as used within a project.	X
3	RepresentationType	IfcLabel	[0:1]	The description of the type of a representation context. The representation type defines the type of geometry or topology used for representing the product representation. More information is given at the subtypes IfcShapeRepresentation and IfcTopologyRepresentation. The supported values for context type are to be specified by implementers agreements.	X
4	Items	IfcRepresentationItem	S[1:?]	Set of geometric representation items that are defined for this representation.	X
	RepresentationMap	IfcRepresentationMap @MappedRepresentation	S[0:1]	Use of the representation within an IfcRepresentationMap. If used, this IfcRepresentation may be assigned to many representations as one of its Items using an IfcMappedItem. Using IfcRepresentationMap is the way to share one representation (often of type IfcShapeRepresentation) by many products.
	OfProductRepresentation	IfcProductRepresentation @Representations	S[0:1]	Reference to the product shape, for which it is the shape representation.
IfcShapeModel
IfcShapeRepresentation

Formal representations

XSD Specification

 <xs:element name="IfcShapeRepresentation" type="ifc:IfcShapeRepresentation" substitutionGroup="ifc:IfcShapeModel" nillable="true"/>

 <xs:complexType name="IfcShapeRepresentation">

  <xs:complexContent>

   <xs:extension base="ifc:IfcShapeModel"/>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcShapeRepresentation

 SUBTYPE OF (IfcShapeModel);

 WHERE

  WR21 : 'IFCREPRESENTATIONRESOURCE.IFCGEOMETRICREPRESENTATIONCONTEXT' 
IN TYPEOF(SELF\IfcRepresentation.ContextOfItems);
  WR22 : SIZEOF(QUERY(temp <* Items | 
  ('IFCTOPOLOGYRESOURCE.IFCTOPOLOGICALREPRESENTATIONITEM' IN TYPEOF(temp))
    AND (NOT(SIZEOF(
      ['IFCTOPOLOGYRESOURCE.IFCVERTEXPOINT',
       'IFCTOPOLOGYRESOURCE.IFCEDGECURVE',
       'IFCTOPOLOGYRESOURCE.IFCFACESURFACE'] * TYPEOF(temp)) = 1))
)) = 0;
  WR23 : EXISTS(SELF\IfcRepresentation.RepresentationType);
  WR24 : IfcShapeRepresentationTypes(SELF\IfcRepresentation.RepresentationType, SELF\IfcRepresentation.Items);
END_ENTITY;

 EXPRESS-G diagram