|modifications||attributes PlacementRefDirection definition||Changed from IfcVirtualGridIntersection to IfcGridPlacementDirectionSelect|
IfcGridPlacement provides a specialization of IfcObjectPlacement in which the placement and axis direction of the object coordinate system is defined by a reference to the design grid as defined in IfcGrid.
The location of the object coordinate system is given by the attribute PlacementLocation. It is defined as an IfcVirtualGridIntersection, that is, an intersection between two grid axes with optional offsets.
The axis direction of the x-axis of the object coordinate system is given either:
The direction of the y-axis of the IfcGridPlacement is the orthogonal complement to the x-axis. The plane defined by the x and y axis shall be co-planar to the xy plane of the local placement of the IfcGrid.
The direction of the z-axis is the orientation of the cross product of the x-axis and the y-axis, i.e. the z-axis of the IfcGridPlacement shall be co-linear to the z-axis of the local placement of the IfcGrid.
NOTE The IfcGrid local placement, that can be provided relative to the local placement of another spatial structure element, has to be taken into account for calculating the absolute placement of the virtual grid intersection.
NOTE The PlacementLocation.OffsetDistances and the PlacementRefDirection.OffsetDistances shall either not be assigned or should have the same z offset value.
The following figures show the usage of placement location and direction for an IfcGridPlacement.
Figure 1 illustrates the case where PlacementRefDirection is not given - the object coordinate system is defined by:
Figure 1 — Grid placement
Figure 2 illustrates the case where PlacementRefDirection is given as an IfcDirection- the object coordinate system is defined by:
Figure 2 — Grid placement with direction
Figure 3 illustrates the case where PlacementRefDirection is given as an IfcVirtualGridIntersection- the object coordinate system is defined by:
Figure 3 — Grid placement with intersection
HISTORY New entity in IFC1.5. The entity name was changed from IfcConstrainedPlacement in IFC2x.
IFC4 CHANGE Attribute data type of PlacementRefDirection has been changed to IfcGridPlacementDirectionSelect.
|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.
> 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.|
|2||PlacementLocation||IfcVirtualGridIntersection||Placement of the object coordinate system defined by the intersection of two grid axes.|
|3||PlacementRefDirection||OPTIONAL IfcGridPlacementDirectionSelect||Reference to either an explicit direction, or a second grid axis intersection, which defines the orientation of the grid placement.|
> IFC4 CHANGE The select of an explict direction has been added.
ENTITY IfcGridPlacement SUBTYPE OF (IfcObjectPlacement); PlacementLocation : IfcVirtualGridIntersection; PlacementRefDirection : OPTIONAL IfcGridPlacementDirectionSelect; END_ENTITY;