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IfcAxis2Placement2D

Definition from ISO/CD 10303-42:1992: The location and orientation in two dimensional space of two mutually perpendicular axes. An axis2_placement_2d (IfcAxis2Placement2D) is defined in terms of a point, (inherited from the IfcPlacement supertype), and an axis. It can be used to locate and originate an object in two dimensional space and to define a placement coordinate system. The class includes a point which forms the origin of the placement coordinate system. A direction vector is required to complete the definition of the placement coordinate system. The reference direction defines the placement X axis direction, the placement Y axis is derived from this.

Definition from IAI: If the RefDirection attribute is not given, the placement defaults to P[1] (x-axis) as [1.,0.] and P[2] (y-axis) as [0.,1.].

NOTE Corresponding STEP name: axis2_placement_2d, please refer to ISO/IS 10303-42:1994, p. 28 for the final definition of the formal standard.

HISTORY New class in IFC Release 1.5, the IFC Release 1.0 entity IfcPlacement_2D was using two normalized and orthogonal axes. This definition is replaced in IFC Release 1.5 by the STEP definition of axis placement.
ISSUE: See issue log for changes made in IFC Release 1.5.1

Illustration

axis2 placement 2D Definition of the IfcAxis2Placement2D within the two-dimensional coordinate system.

EXPRESS specification:

ENTITY IfcAxis2Placement2D
SUBTYPE OF ( IfcPlacement);
RefDirection  :  OPTIONAL IfcDirection;
DERIVE
P  :  LIST [2:2] OF IfcDirection :=  IfcBuild2Axes(RefDirection);
WHERE
WR1  :  (NOT (EXISTS (RefDirection))) OR (RefDirection.Dim = 2);
WR2  :  SELF\IfcPlacement.Location.Dim = 2;
END_ENTITY;

Attribute definitions:

RefDirection  :  The direction used to determine the direction of the local X Axis.
P  :  P[1]: The normalized direction of the placement X Axis. This is (1.0,0.0,0.0) if RefDirection is omitted. P[2]: The normalized direction of the placement Y Axis. This is a derived attribute and is orthogonal to P[1].

References (2):

Name Type Referred through Express-G
IfcAxis2Placement Select
Select relation
Diagram 3
IfcPlacement Entity
Subtype
Diagram 3

Inheritance graph

ENTITY IfcAxis2Placement2D;
ENTITY IfcRepresentationItem;
ENTITY IfcGeometricRepresentationItem;
ENTITY IfcPlacement;
Location  :  IfcCartesianPoint;
DERIVE
Dim  :  IfcDimensionCount :=  Location.Dim;
ENTITY IfcAxis2Placement2D;
RefDirection  :  OPTIONAL IfcDirection;
DERIVE
P  :  LIST [2:2] OF IfcDirection :=  IfcBuild2Axes(RefDirection);
END_ENTITY;