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IfcPlacement

Definition from ISO/CD 10303-42:1992: A placement entity defines the local environment for the definition of a geometry item. It locates the item to be defined and, in the case of the axis placement subtypes, gives its orientation.

Additional definition from ISO/WD SC4/WG12/N071 Part42.2 geometry_schema: A placement locates a geometric item with respect to the coordinate system of its geometric context.

Definition from IAI: The IfcPlacement is an abstract supertype not to be directly instantiated, whereas the STEP P42 entity placement can be instantiated to define a placement without orientation. The derived attribute Dim has been added, see also note at IfcGeometricRepresentationItem.

NOTE Corresponding STEP entity: placement, in contrary to IFC Release 1.0 the IfcPlacement definition in IFC Release 1.5 strictly follows the STEP definition. Please refer to ISO/IS 10303-42:1994, p. 27 for the final definition of the formal standard.

HISTORY New class in IFC Release 1.0


EXPRESS specification:

ENTITY IfcPlacement
ABSTRACT SUPERTYPE OF (ONEOF(IfcAxis1Placement, IfcAxis2Placement2D, IfcAxis2Placement3D))
SUBTYPE OF ( IfcGeometricRepresentationItem);
Location  :  IfcCartesianPoint;
DERIVE
Dim  :  IfcDimensionCount :=  Location.Dim;
END_ENTITY;

Attribute definitions:

Location  :  The geometric position of a reference point, such as the center of a circle, of the item to be located.
Dim  :  The space dimensionality of this class, derived from the dimensionality of the location.

References (4):

Name Type Referred through Express-G
IfcAxis1Placement Entity
Supertype
Diagram 3
IfcAxis2Placement2D Entity
Supertype
Diagram 3
IfcAxis2Placement3D Entity
Supertype
Diagram 3
IfcGeometricRepresentationItem Entity
Subtype
Diagram 1

Inheritance graph

ENTITY IfcPlacement;
ENTITY IfcRepresentationItem;
ENTITY IfcGeometricRepresentationItem;
ENTITY IfcPlacement;
Location  :  IfcCartesianPoint;
DERIVE
Dim  :  IfcDimensionCount :=  Location.Dim;
END_ENTITY;