IfcAxis2Placement3D
Definition
from ISO/CD 1030342:1992: The
location and orientation in three dimensional space of three mutually
perpendicular axes. An axis2_placement_3D is defined in terms of a
point (inherited from placement supertype) and two (ideally orthogonal)
axes. It can be used to locate and originate an object in three
dimensional space and to define a placement coordinate system. The
entity includes a point which forms the origin of the placement
coordinate system. Two direction vectors are required to complete the
definition of the placement coordinate system. The axis is the
placement Z axis direction and the ref_direction is an approximation to
the placement X axis direction.
Definition from buildingSMART: If the attribute
values for Axis and RefDirection
are not given, the placement defaults to P[1] (xaxis) as [1.,0.,0.],
P[2] (yaxis) as [0.,1.,0.] and P[3] (zaxis) as [0.,0.,1.].
NOTE
Corresponding STEP name: axis2_placement_3d, please refer to ISO/IS
1030342:1994 for the final definition of the formal standard. The WR5
is added to ensure that either both attributes Axis
and RefDirection are given, or both are omitted.
HISTORY
New entity in IFC Release 1.5.
Illustration

Definition of the IfcAxis2Placement3D
within the threedimensional coordinate system. 
EXPRESS specification:



P

:

LIST [3:3] OF IfcDirection := IfcBuildAxes(Axis, RefDirection);



WR1

:

SELF\IfcPlacement.Location.Dim = 3;

WR2

:

(NOT (EXISTS (Axis))) OR (Axis.Dim = 3);

WR3

:

(NOT (EXISTS (RefDirection))) OR (RefDirection.Dim = 3);

WR4

:

(NOT (EXISTS (Axis))) OR (NOT (EXISTS (RefDirection))) OR (IfcCrossProduct(Axis,RefDirection).Magnitude > 0.0);

WR5

:

NOT ((EXISTS (Axis)) XOR (EXISTS (RefDirection)));




Attribute definitions:
Axis

:

The exact direction of the local Z Axis.

RefDirection

:

The direction used to determine the direction of the local X Axis. If necessary an adjustment is made
to maintain orthogonality to the Axis direction. If Axis and/or RefDirection is omitted, these directions
are taken from the geometric coordinate system.

P

:

The normalized directions of the placement X Axis (P[1]) and the placement Y Axis (P[2]) and the placement
Z Axis (P[3]).

Formal Propositions:
WR1

:

The dimensionality of the placement location shall be 3.

WR2

:

The Axis when given should only reference a threedimensional IfcDirection.

WR3

:

The RefDirection when given should only reference a threedimensional IfcDirection.

WR4

:

The Axis and RefDirection shall not be parallel or antiparallel.

WR5

:

Either both (Axis and RefDirection) are not given and therefore defaulted, or both shall be given. This
is a further constraint in IFC Release 1.5.

Inheritance graph

ENTITY IfcAxis2Placement3D;



P

:

LIST [3:3] OF IfcDirection := IfcBuildAxes(Axis, RefDirection);



