8.9.3.4 IfcAxis2PlacementLinear

8.9.3.4.1 Semantic definition

The IfcAxis2PlacementLinear provides location and orientation to place items in a three-dimensional space confined to the context of a curve. Relative placement axes (Axis and RefDirection) are relative to the curve used for linear referencing provided in IfcPlacement Location (IfcPointByDistanceExpression BasisCurve), maintaining the relationship to the tangent of the curve.

8.9.3.4.2 Entity inheritance

8.9.3.4.3 Attributes

#	Attribute	Type	Description
IfcRepresentationItem (2)
	LayerAssignment	SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems	Assignment of the representation item to a single or multiple layer(s). The LayerAssignments can override a LayerAssignments of the IfcRepresentation it is used within the list of Items. IFC2x3-CHANGE The inverse attribute LayerAssignments has been added. IFC4-CHANGE The inverse attribute LayerAssignment has been restricted to max 1. Upward compatibility for file based exchange is guaranteed.
	StyledByItem	SET [0:1] OF IfcStyledItem FOR Item	Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve. IFC2x3-CHANGE The inverse attribute StyledByItem has been added.
IfcPlacement (2)
1	Location	IfcPoint	The geometric position of a reference point, such as the center of a circle, of the item to be located.
*	Dim	IfcDimensionCount	This attribute is formally derived. `Location.Dim` The space dimensionality of this class, derived from the dimensionality of the location.
Click to show 4 hidden inherited attributes Click to hide 4 inherited attributes
IfcAxis2PlacementLinear (2)
2	Axis	OPTIONAL IfcDirection	The exact direction of the local Z Axis.
3	RefDirection	OPTIONAL IfcDirection	The direction used to determine the direction of the local X Axis. In case both Axis and RefDirection are set and not perpendicular an adjustment is necessary to maintain orthogonality to the Axis direction. If RefDirection is omitted, the direction is taken from the curve tangent at Location.

Table 8.9.3.4.B

8.9.3.4.4 Formal propositions

Name	Description
WR1	The Location on parent type IfcPlacement shall be of type IfcPointByDistanceExpression
`'IFC4X3.IFCPOINTBYDISTANCEEXPRESSION' IN TYPEOF(SELF\IfcPlacement.Location)`
WR2	The Axis and RefDirection shall not be parallel or anti-parallel.
`(NOT (EXISTS (Axis))) OR (NOT (EXISTS (RefDirection))) OR (IfcCrossProduct(Axis,RefDirection).Magnitude > 0.0)`

Table 8.9.3.4.C

8.9.3.4.5 Examples

Figure 8.9.3.4.A

LinearPlacement_2

8.9.3.4.6 Formal representation

ENTITY IfcAxis2PlacementLinear
 SUBTYPE OF (IfcPlacement);
	Axis : OPTIONAL IfcDirection;
	RefDirection : OPTIONAL IfcDirection;
 WHERE
	WR1 : 'IFC4X3.IFCPOINTBYDISTANCEEXPRESSION' IN TYPEOF(SELF\IfcPlacement.Location);
	WR2 : (NOT (EXISTS (Axis))) OR (NOT (EXISTS (RefDirection))) OR (IfcCrossProduct(Axis,RefDirection).Magnitude > 0.0);
END_ENTITY;