IfcGridPlacement

Natural language names
Rasterplatzierung
Grid Placement
Positionnement de grille
Change log
ItemSPFXMLChangeDescription
IFC2x3 to IFC4
    IfcGridPlacement
      PlacementRefDirectionMODIFIEDType changed from IfcVirtualGridIntersection to IfcGridPlacementDirectionSelect.
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:

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.

without ref direction

Figure 318 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 318 — Grid placement

  
with ref direction

Figure 319 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 319 — Grid placement with direction

  
with ref direction

Figure 320 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 320 — 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
#AttributeTypeCardinalityDescription G
1PlacementLocationIfcVirtualGridIntersection Placement of the object coordinate system defined by the intersection of two grid axes. X
2PlacementRefDirectionIfcGridPlacementDirectionSelect? 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 IfcObjectPlacement
Attribute inheritance
#AttributeTypeCardinalityDescriptionG
IfcObjectPlacement
PlacesObjectIfcProduct
@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
ReferencedByPlacementsIfcLocalPlacement
@PlacementRelTo		S[0:?]Placements that are given relative to this placement of an object.X
IfcGridPlacement
1PlacementLocationIfcVirtualGridIntersection Placement of the object coordinate system defined by the intersection of two grid axes. X
2PlacementRefDirectionIfcGridPlacementDirectionSelect? 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
Examples
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;

Link to EXPRESS-G diagram EXPRESS-G diagram

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