IFC 4.3.x development

8.7.3.18 IfcObjectPlacement

Change log

IFC4

modificationsinverses PlacesObject definitionChanged from SET OF [1:1] IfcProduct FOR ObjectPlacement to SET OF [0:?] IfcProduct FOR ObjectPlacement

IFC4X2

additionsattributesPlacementRelTo

8.7.3.18.1 Semantic definitions at the entity

IfcObjectPlacement is an abstract supertype for the special types defining the object coordinate system. The IfcObjectPlacement has to be provided for each product that has a shape representation.

The object placement can be given:

  • absolute: by an axis2 placement, relative to the world coordinate system,
  • relative: by an axis2 placement, relative to the object placement of another product,
  • by grid reference: by the virtual intersection and reference direction given by two axes of a design grid,
  • linear placement: by distance along a curve, with possible offsets.

In any case the object placement has to unambiguously define the object coordinate system as either two-dimensional axis placement (IfcAxis2Placement2D) or three-dimensional axis placement (IfcAxis2Placement3D). The axis placement may have to be calculated.

HISTORY  New entity in IFC2x.

8.7.3.18.1 Attributes

# Attribute Type Description
IfcObjectPlacement
PlacesObject SET [0:?] OF IfcProduct FOR ObjectPlacementThe IfcObjectPlacement shall be used to provide a placement and

an object coordinate system for instances of IfcProduct.

> If an IfcObjectPlacement is shared by many instances of IfcProduct it does not apply a semantic meaning of being a shared placement that needs to be maintained. The same instance of IfcObjectPlacement could simply be used to reduce exchange file size.

> IFC2x3 CHANGE  New inverse attribute.

> IFC4 CHANGE  The cardinality has changed to 0..n to allow reuse of instances of IfcObjectPlacement as placement object in one to many products. It takes also into account that it can act as a placement for IfcStructuralAnalysisModel.
1 PlacementRelToOPTIONAL IfcObjectPlacement Reference to object placement that provides the relative placement with its placement in a grid, local coordinate system or linear referenced placement. If it is omitted, then in the case of linear placement it is established by the origin of horizontal alignment of the referenced IfcAlignment Axis. In the case of local placement it is established by the geometric representation context.

8.7.3.18.2 Entity inheritance

dot_inheritance IfcGridPlacement IfcGridPlacement IfcObjectPlacement IfcObjectPlacement IfcGridPlacement->IfcObjectPlacement IfcLinearPlacement IfcLinearPlacement IfcLinearPlacement->IfcObjectPlacement IfcLocalPlacement IfcLocalPlacement IfcLocalPlacement->IfcObjectPlacement

8.7.3.18.3 Formal representations

ENTITY IfcObjectPlacement
 ABSTRACT SUPERTYPE OF (ONEOF
	(IfcGridPlacement
	,IfcLinearPlacement
	,IfcLocalPlacement));
	PlacementRelTo : OPTIONAL IfcObjectPlacement;
 INVERSE
	PlacesObject : SET [0:?] OF IfcProduct FOR ObjectPlacement;
END_ENTITY;