IfcGridPlacement

Item	SPF	XML	Change	Description
IFC2x3 to IFC4 4.0.0.0
IfcGridPlacement
PlacementRefDirection			MODIFIED	Type changed from IfcVirtualGridIntersection to IfcGridPlacementDirectionSelect.
IFC4x2 Candidate 4.2.0.0
IfcGridPlacement
PlacementRelTo	X	X	MODIFIED	Name changed from PlacementLocation to PlacementRelTo. Type changed from IfcVirtualGridIntersection to IfcObjectPlacement. Instantiation changed to OPTIONAL. Xsdformat changed from Attribute to Default.
PlacementLocation	X	X	MODIFIED	Name changed from PlacementRefDirection to PlacementLocation. Type changed from IfcGridPlacementDirectionSelect to IfcVirtualGridIntersection. Instantiation changed from OPTIONAL. Xsdformat changed from Default to Attribute.
PlacementRefDirection			ADDED
ReferencedByPlacements			DELETED

Semantic definitions at the entity

Entity definition

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:

PlacementRefDirection = NIL: by the tangent of the first grid axis (PlacementLocation.IntersectingAxes[1]) at the virtual intersection (maybe using the offset curve, if PlacementLocation.OffsetDistances is given);
PlacementRefDirection = IfcDirection: by the explicitly provided direction information;
PlacementRefDirection = IfcVirtualGridIntersection: by the tangent between the virtual grid intersection of PlacementLocation and the virtual grid intersection of PlacementRefDirection. Offsets as potentially provided in the IfcVirtualGridIntersection's of PlacementLocation and PlacementRefDirection have to be taken into account.

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[3] and the PlacementRefDirection.OffsetDistances[3] 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 465 illustrates the case where PlacementRefDirection is not given - the object coordinate system is defined by:

its location: given by the virtual grid intersection of PlacementLocation
its x-axis direction: given by the tangent of the first intersecting axis in the offset location of the virtual grid intersection

Figure 465 — Grid placement

Figure 466 illustrates the case where PlacementRefDirection is given as an IfcDirection- the object coordinate system is defined by:

its location: given by the virtual grid intersection of PlacementLocation
its x-axis direction: given by the DirectionRatios of the IfcDirection, only the ratios for x and y are taken into account,

Figure 466 — Grid placement with direction

Figure 467 illustrates the case where PlacementRefDirection is given as an IfcVirtualGridIntersection- the object coordinate system is defined by:

its location: given by the virtual grid intersection of PlacementLocation
its x-axis direction: given by the tangent of the line between the virtual grid intersection of the PlacementLocation and the virtual grid intersection of the PlacementRefDirection.

Figure 467 — 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.

Attribute definitions

#	Attribute	Type	Cardinality	Description	G
2	PlacementLocation	IfcVirtualGridIntersection		Placement of the object coordinate system defined by the intersection of two grid axes.	X
3	PlacementRefDirection	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.	X

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	G
IfcObjectPlacement
1	PlacementRelTo	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.	X
	PlacesObject	IfcProduct @ObjectPlacement	S[0:?]	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.	X
	ReferencedByPlacements	IfcObjectPlacement @PlacementRelTo	S[0:?]	Placements that are given relative to this placement of an object.	X
IfcGridPlacement
2	PlacementLocation	IfcVirtualGridIntersection		Placement of the object coordinate system defined by the intersection of two grid axes.	X
3	PlacementRefDirection	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.	X

Formal representations

XML Specification

 <xs:element name="IfcGridPlacement" type="ifc:IfcGridPlacement" substitutionGroup="ifc:IfcObjectPlacement" nillable="true"/>

 <xs:complexType name="IfcGridPlacement">

  <xs:complexContent>

   <xs:extension base="ifc:IfcObjectPlacement">

    <xs:sequence>

     <xs:element name="PlacementLocation" type="ifc:IfcVirtualGridIntersection" nillable="true"/>

     <xs:element name="PlacementRefDirection" nillable="true" minOccurs="0">

      <xs:complexType>

       <xs:group ref="ifc:IfcGridPlacementDirectionSelect"/>

      </xs:complexType>

     </xs:element>

    </xs:sequence>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcGridPlacement

 SUBTYPE OF (IfcObjectPlacement);

  PlacementLocation : IfcVirtualGridIntersection;

  PlacementRefDirection : OPTIONAL IfcGridPlacementDirectionSelect;

END_ENTITY;

 EXPRESS-G diagram

	Rasterplatzierung
	Grid Placement
	Positionnement de grille