IFC 4.3.x development

8.7.3.14 IfcLocalPlacement

Change log

IFC4X2

deletionsattributesPlacementRelTo

8.7.3.14.1 Semantic definitions at the entity

An IfcLocalPlacement defines the relative placement of a product in relation to the placement of another product or the absolute placement of a product within the geometric representation context of the project.

The IfcLocalPlacement allows that an IfcProduct can be placed by this IfcLocalPlacement (through the attribute_ObjectPlacement_) within the local coordinate system of the object placement of another IfcProduct, which is referenced by the PlacementRelTo. Rules to prevent cyclic relative placements have to be introduced on the application level.

If the PlacementRelTo is not given, then the IfcProduct is placed absolutely within the world coordinate system.

The following conventions shall apply as default relative positions if the relative placement is used. The conventions are given for all five direct subtypes of IfcProduct, the IfcSpatialStructureElement, IfcElement, IfcAnnotation, IfcGrid, IfcPort. More detailed placement information is given at the level of subtypes of those five types mentioned.

HISTORY  New entity in IFC1.0.

8.7.3.14.1 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 PlacementRelTo OPTIONAL 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.
IfcLocalPlacement
2 RelativePlacementIfcAxis2Placement Geometric placement that defines the transformation from the related coordinate system into the relating. The placement can be either 2D or 3D, depending on the dimension count of the coordinate system.

8.7.3.14.2 Entity inheritance

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

8.7.3.14.3 Formal representations

ENTITY IfcLocalPlacement
 SUBTYPE OF (IfcObjectPlacement);
	RelativePlacement : IfcAxis2Placement;
 WHERE
	WR21 : IfcCorrectLocalPlacement(RelativePlacement, PlacementRelTo);
END_ENTITY;