IFC 4.3.x development

8.9.3.60 IfcRepresentationItem

Change log

IFC4

modificationsinverses LayerAssignments definitionChanged from SET OF [0:?] IfcPresentationLayerAssignment FOR AssignedItems to SET OF [0:1] IfcPresentationLayerAssignment FOR AssignedItems
modificationsinverses LayerAssignments name Changed from LayerAssignments to LayerAssignment

8.9.3.60.1 Semantic definitions at the entity

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 1 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 2 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"

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.

8.9.3.60.1 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.

8.9.3.60.2 Entity inheritance

dot_inheritance IfcRepresentationItem_children 3 more... IfcRepresentationItem IfcRepresentationItem IfcRepresentationItem_children->IfcRepresentationItem

8.9.3.60.3 Formal representations

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;