IfcGeometricRepresentationContext

Semantic definitions at the entity

Entity definition

Definition from ISO/CD 10303-42:1992: A geometric representation context is a representation context in which the geometric representation items are geometrically founded. A geometric representation context is a distinct coordinate space, spatially unrelated to other coordinate spaces.

Definition from IAI: The IfcGeometricRepresentationContext defines the context that applies to several shape representations of products within a project. It defines the type of the context in which the shape representation is defined, and the numeric precision applicable to the geometric representation items defined in this context. In addition it can be used to offset the project coordinate system from a global point of origin, using the WorldCoordinateSystem attribute. The TrueNorth attribute can be given, if the y axis of the WorldCoordinateSystem does not point to the global northing.

NOTE The inherited attribute ContextType shall have one of the following recognized values: ~~'Sketch', 'Outline', 'Design', 'Detail',~~ 'Model', 'Plan', 'NotDefined'.

The use of one instance of IfcGeometricRepresentationContext to represent the model (3D) view is mandatory, the use of a second instance of IfcGeometricRepresentationContext to represent the plan (2D) view is optional (but needs to be given, if there are scale dependent plan views), the additional scale or view dependent contexts need to be handled by using the subtype IfcGeometricRepresentationSubContext pointing to the model view (or the plan view) as the ParentContext.

NOTE The definition of this class relates to the STEP entity geometric_representation_context. Please refer to ISO/IS 10303-42:1994 for the final definition of the formal standard.

HISTORY New Entity in IFC Release 2.0
IFC2x Edition 3 CHANGE Applicable values for ContextType are only 'Model', 'Plan', and 'NotDefined'. All other sub contexts are now handled by the new subtype in IFC2x Edition 2 IfcGeometricRepresentationSubContext. Upward compatibility for file based exchange is guaranteed.

Attribute definitions

#	Attribute	Type	Cardinality	Description	A
3	CoordinateSpaceDimension	IfcDimensionCount	[1:1]	The integer dimension count of the coordinate space modeled in a geometric representation context.	X
4	Precision	-		This attribute is out of scope for this model view definition and shall not be set.
5	WorldCoordinateSystem	IfcAxis2Placement	[1:1]	Establishment of the engineering coordinate system (often referred to as the world coordinate system in CAD) for all representation contexts used by the project. Note it can be used to provide better numeric stability if the placement of the building(s) is far away from the origin. In most cases however it would be set to origin: (0.,0.,0.) and directions x(1.,0.,0.), y(0.,1.,0.), z(0.,0.,1.).	X
6	TrueNorth	IfcDirection	[0:1]	Direction of the true north relative to the underlying coordinate system as established by the attribute WorldCoordinateSystem. It is given by a direction within the xy-plane of the underlying coordinate system. If not given, it defaults to the positive direction of the y-axis of the WorldCoordinateSystem.	X
	HasSubContexts	IfcGeometricRepresentationSubContext @ParentContext	S[0:?]	The set of IfcGeometricRepresentationSubContexts that refer to this IfcGeometricRepresentationContext.	X

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	A
IfcRepresentationContext
1	ContextIdentifier	IfcLabel	[0:1]	The optional identifier of the representation context as used within a project.	X
2	ContextType	IfcLabel	[0:1]	The description of the type of a representation context. The supported values for context type are to be specified by implementers agreements.	X
	RepresentationsInContext	IfcRepresentation @ContextOfItems	S[0:?]	All shape representations that are defined in the same representation context.
IfcGeometricRepresentationContext
3	CoordinateSpaceDimension	IfcDimensionCount	[1:1]	The integer dimension count of the coordinate space modeled in a geometric representation context.	X
4	Precision	-		This attribute is out of scope for this model view definition and shall not be set.
5	WorldCoordinateSystem	IfcAxis2Placement	[1:1]	Establishment of the engineering coordinate system (often referred to as the world coordinate system in CAD) for all representation contexts used by the project. Note it can be used to provide better numeric stability if the placement of the building(s) is far away from the origin. In most cases however it would be set to origin: (0.,0.,0.) and directions x(1.,0.,0.), y(0.,1.,0.), z(0.,0.,1.).	X
6	TrueNorth	IfcDirection	[0:1]	Direction of the true north relative to the underlying coordinate system as established by the attribute WorldCoordinateSystem. It is given by a direction within the xy-plane of the underlying coordinate system. If not given, it defaults to the positive direction of the y-axis of the WorldCoordinateSystem.	X
	HasSubContexts	IfcGeometricRepresentationSubContext @ParentContext	S[0:?]	The set of IfcGeometricRepresentationSubContexts that refer to this IfcGeometricRepresentationContext.	X

Formal representations

XSD Specification

 <xs:element name="IfcGeometricRepresentationContext" type="ifc:IfcGeometricRepresentationContext" substitutionGroup="ifc:IfcRepresentationContext" nillable="true"/>

 <xs:complexType name="IfcGeometricRepresentationContext">

  <xs:complexContent>

   <xs:extension base="ifc:IfcRepresentationContext">

    <xs:sequence>

     <xs:element name="WorldCoordinateSystem" minOccurs="0">

      <xs:complexType>

       <xs:group ref="ifc:IfcAxis2Placement"/>

      </xs:complexType>

     </xs:element>

     <xs:element name="TrueNorth" type="ifc:IfcDirection" nillable="true" minOccurs="0"/>

    </xs:sequence>

    <xs:attribute name="CoordinateSpaceDimension" type="ifc:IfcDimensionCount" use="optional"/>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcGeometricRepresentationContext

 SUPERTYPE OF(IfcGeometricRepresentationSubContext)

 SUBTYPE OF (IfcRepresentationContext);

  CoordinateSpaceDimension : IfcDimensionCount;

  Precision : OPTIONAL IfcStrippedOptional;

  WorldCoordinateSystem : IfcAxis2Placement;

  TrueNorth : OPTIONAL IfcDirection;

 INVERSE

  HasSubContexts : SET [0:?] OF IfcGeometricRepresentationSubContext FOR ParentContext;

END_ENTITY;

 EXPRESS-G diagram