8.9.3.3 IfcAxis2Placement3D

Einfügepunkt mit zwei Achsen - dreidimensionaler Raum (3D)

The IfcAxis2Placement3D provides location and orientations to place items in a three-dimensional space. The attribute Axis defines the Z direction, RefDirection the X direction. The Y direction is derived.

NOTE  The RefDirection does not have to be orthogonal to Axis.

If the attribute values for Axis and RefDirection are not given, the placement defaults to P[1] (x-axis) as [1.,0.,0.], P[2] (y-axis) as [0.,1.,0.] and P[3] (z-axis) as [0.,0.,1.].

axis2 placement 2D
Figure 314 illustrates the definition of the IfcAxis2Placement3D within the three-dimensional coordinate system.

Figure 314 — Axis2 placement 3D

 
NOTE  Definition according to ISO/CD 10303-42:1992
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 orientate a non axi-symmetric object in 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.
NOTE  Entity adapted from axis2_placement_3d defined in ISO10303-42.
HISTORY  New entity in IFC1.5.

XSD Specification:

 <xs:element name="IfcAxis2Placement3D" type="ifc:IfcAxis2Placement3D" substitutionGroup="ifc:IfcPlacement" nillable="true"/>
 <xs:complexType name="IfcAxis2Placement3D">
  <xs:complexContent>
   <xs:extension base="ifc:IfcPlacement">
    <xs:sequence>
     <xs:element name="Axis" type="ifc:IfcDirection" nillable="true" minOccurs="0"/>
     <xs:element name="RefDirection" type="ifc:IfcDirection" nillable="true" minOccurs="0"/>
    </xs:sequence>
   </xs:extension>
  </xs:complexContent>
 </xs:complexType>

EXPRESS Specification:

ENTITY IfcAxis2Placement3D
SUBTYPE OF IfcPlacement;
Axis : OPTIONAL IfcDirection;
RefDirection : OPTIONAL IfcDirection;
DERIVE
P : LIST [3:3] OF IfcDirection := IfcBuildAxes(Axis, RefDirection);
WHERE
LocationIs3D : SELF\IfcPlacement.Location.Dim = 3;
AxisIs3D : (NOT (EXISTS (Axis))) OR (Axis.Dim = 3);
RefDirIs3D : (NOT (EXISTS (RefDirection))) OR (RefDirection.Dim = 3);
AxisToRefDirPosition : (NOT (EXISTS (Axis))) OR (NOT (EXISTS (RefDirection))) OR (IfcCrossProduct(Axis,RefDirection).Magnitude > 0.0);
AxisAndRefDirProvision : NOT ((EXISTS (Axis)) XOR (EXISTS (RefDirection)));
END_ENTITY;

Link to EXPRESS-G diagram EXPRESS-G diagram

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:

LocationIs3D : The dimensionality of the placement location shall be 3.
AxisIs3D : The Axis when given should only reference a three-dimensional IfcDirection.
RefDirIs3D : The RefDirection when given should only reference a three-dimensional IfcDirection.
AxisToRefDirPosition : The Axis and RefDirection shall not be parallel or anti-parallel.
AxisAndRefDirProvision : Either both, Axis and RefDirection are not given and therefore defaulted, or both shall be given.

Inheritance Graph:

ENTITY IfcAxis2Placement3D
ENTITY IfcRepresentationItem
INVERSE
LayerAssignment : SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems;
StyledByItem : SET [0:1] OF IfcStyledItem FOR Item;
ENTITY IfcGeometricRepresentationItem
ENTITY IfcPlacement
Location : IfcCartesianPoint;
DERIVE
Dim : IfcDimensionCount := Location.Dim;
ENTITY IfcAxis2Placement3D
Axis : OPTIONAL IfcDirection;
RefDirection : OPTIONAL IfcDirection;
DERIVE
P : LIST [3:3] OF IfcDirection := IfcBuildAxes(Axis, RefDirection);
END_ENTITY;

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