8.9.3.46 IfcRepresentationItem

Item de représentation
Repräsentationselement

The IfcRepresentationItem is used within an IfcRepresentation (directly or indirectly through other IfcRepresentationItem's) to represent an IfcProductRepresentation. Most commonly these IfcRepresentationItem's are geometric or topological representation items, that can (but not need to) have presentation style infomation assigned.

NOTE  Definition according to ISO/CD 10303-43:1992
A representation item is an element of product data that participates in one or more representations or contributes to the definition of another representation item. A representation item contributes to the definition of another representation item when it is referenced by that representation item.
NOTE  The assignment of a style is only applicable to the subtypes IfcGeometricRepresentationItem, IfcMappedItem and some selected subtypes of IfcTopologicalRepresentationItem (IfcVertexPoint, IfcEdgeCurve, IfcFaceSurface).

In case that presentation style information is applied, it can be either applied by an IfcStyledItem, or by an assignment to an IfcPresentationLayerWithStyle. If both are present, and both style assignments include the same subtype of IfcPresentationStyle, then the style assigned by IfcStyledItem takes priority.

Figure 322 shows an instance diagram explaining the use of IfcStyledItem and IfcPresentationLayerWithStyle to apply presentation styles.

EXAMPLE  The assignment of style information by a styled item and a presentation layer with style. Since the presentation styles are different, IfcCurveStyle and IfcSurfaceStyle, both are applied to the geometric representation item.
styles assigned by layer and styled item

Figure 322 — Representation item style

Figure 323 shows in instance diagram explaining the override of IfcPresentationLayerWithStyle by IfcStyledItem to apply presentation styles.

EXAMPLE  The assignment of style information by a styled item and a presentation layer with style. Since the presentation styles for curve style are aprovided by both, the IfcCurveStyle provided by the IfcStyledItem overrides the IfcCurveStyle provided by the IfcPresentationLayerWithStyle
styles assigned by layer and styled item

Figure 323 — Representation item style override

NOTE  Entity adapted from representation_map defined in ISO 10303-43.
HISTORY  New entity in IFC2x.
IFC2x3 CHANGE  The inverse attributes StyledByItem and LayerAssignments have been added. Upward compatibility for file based exchange is guaranteed.

XSD Specification:

 <xs:element name="IfcRepresentationItem" type="ifc:IfcRepresentationItem" abstract="true" substitutionGroup="ifc:Entity" nillable="true"/>
 <xs:complexType name="IfcRepresentationItem" abstract="true">
  <xs:complexContent>
   <xs:extension base="ifc:Entity">
    <xs:sequence>
     <xs:element name="StyledByItem" type="ifc:IfcStyledItem" nillable="true" minOccurs="0" maxOccurs="1"/>
    </xs:sequence>
   </xs:extension>
  </xs:complexContent>
 </xs:complexType>

EXPRESS Specification:

ENTITY IfcRepresentationItem
ABSTRACT SUPERTYPE OF(ONEOF(IfcGeometricRepresentationItem, IfcMappedItem, IfcStyledItem, IfcTopologicalRepresentationItem));
INVERSE
LayerAssignment : SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems;
StyledByItem : SET [0:1] OF IfcStyledItem FOR Item;
END_ENTITY;

Link to EXPRESS-G diagram EXPRESS-G diagram

Attribute Definitions:

LayerAssignment : 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.
StyledByItem : 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.

Inheritance Graph:

ENTITY IfcRepresentationItem
ENTITY IfcRepresentationItem
INVERSE
LayerAssignment : SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems;
StyledByItem : SET [0:1] OF IfcStyledItem FOR Item;
END_ENTITY;

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