8.7.3.8 IfcGridPlacement

Positionnement de grille
Rasterplatzierung

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 275 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 275 — Grid placement

 
with ref direction

Figure 276 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 276 — Grid placement with direction

 
with ref direction

Figure 277 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 277 — 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.

XSD 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

Attribute Definitions:

PlacementLocation : Placement of the object coordinate system defined by the intersection of two grid axes.
PlacementRefDirection : 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.

Inheritance Graph:

ENTITY IfcGridPlacement
ENTITY IfcObjectPlacement
INVERSE
PlacesObject : SET [0:?] OF IfcProduct FOR ObjectPlacement;
ReferencedByPlacements : SET OF IfcLocalPlacement FOR PlacementRelTo;
ENTITY IfcGridPlacement
PlacementLocation : IfcVirtualGridIntersection;
PlacementRefDirection : OPTIONAL IfcGridPlacementDirectionSelect;
END_ENTITY;

Link to this page  Link to this page