8.7.3.14 IfcLocalPlacement

RV ⓘ

AbV ⓘ

8.7.3.14.1 Semantic definition

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.

For the subtypes of IfcSpatialStructureElement the following conventions apply
- IfcSite shall be placed absolutely within the world coordinate system established by the geometric representation context of the IfcProject
- IfcFacility shall be placed relative to the local placement of IfcSite
- IfcFacilityPart shall be placed relative to the local placement of IfcFacility
For IfcGrid and IfcAnnotation the convention applies that it shall be placed relative
- to the local placement of its container, either IfcSite, IfcBuilding, or IfcBuildingStorey
  - it should be the same container element that is referenced by the IfcRelContainedInSpatialStructure containment relationship,
For IfcAlignment placed relative to the world coordinate system of IfcProject.
For IfcPort the convention applies that it shall be placed relative
- to the local placement of the IfcElement it belongs to
  - it should be the same element that is referenced by the IfcRelConnectsPortToElement connection relationship,
For IfcElement the convention applies that it shall be placed relative:
- to the local placement of its container, either IfcSite, IfcFacility, or IfcFacilityPart
  - it should be the same container element that is referenced by the IfcRelContainedInSpatialStructure containment relationship,
- to the local placement of the IfcElement to which it is tied by an element composition relationship
  - for features that are located relative to the main component (such as openings), as expressed by IfcRelVoidsElement and IfcRelProjectsElement;
  - for elements that fill an opening (such as doors or windows), as expressed by IfcRelFillsElement;
  - for coverings that cover the element, as expressed by IfcRelCoversBldgElements;
  - for sub components that are aggregated to the main component, as expressed by IfcRelAggregates and IfcRelNests.

8.7.3.14.2 Entity inheritance

- IfcObjectPlacement

8.7.3.14.3 Attributes

#	Attribute	Type	Description
IfcObjectPlacement (3)
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.
	PlacesObject	SET [0:?] OF IfcProduct FOR ObjectPlacement	The IfcObjectPlacement shall be used to provide a placement and an object coordinate system for instances of IfcProduct. 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. 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.
	ReferencedByPlacements	SET [0:?] OF IfcObjectPlacement FOR PlacementRelTo	No description available.
Click to show 3 hidden inherited attributes Click to hide 3 inherited attributes
IfcLocalPlacement (1)
2	RelativePlacement	IfcAxis2Placement	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.

Table 8.7.3.14.A

8.7.3.14.4 Formal propositions

Name	Description
WR21	Ensures that a 3D local placement can only be relative (if exists) to a 3D parent local placement (and not to a 2D parent local placement).
`IfcCorrectLocalPlacement(RelativePlacement, PlacementRelTo)`

Table 8.7.3.14.B

8.7.3.14.5 Formal representation

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