IfcLinearPlacement provides a specialization of IfcObjectPlacement in which the placement and axis direction of the object coordinate system is defined by a reference to a curve. RelativePlacement is therefore restricted to IfcAxis2PlacementLinear.
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.
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.
Placement that provides location and orientation confined to the context of a curve. Linear placement is 3D in nature even in case of a 2D basis curve.
