IfcCartesianTransformationOperator

Semantic definitions at the entity

Entity definition

Definition from ISO/CD 10303-42:1992: A Cartesian transformation operator defines a geometric transformation composed of translation, rotation, mirroring and uniform scaling. The list of normalized vectors u defines the columns of an orthogonal matrix T. These vectors are computed, by the base axis function, from the direction attributes axis1, axis2 and, in Cartesian transformation operator 3d, axis3. If |T|= -1, the transformation includes mirroring. The local origin point A, the scale value S and the matrix T together define a transformation.

The transformation for a point with position vector P is defined by

P -> A + STP

The transformation for a direction d is defined by

d -> Td

The transformation for a vector with orientation d and magnitude k is defined by

d -> Td, and

k -> Sk

For those entities whose attributes include an axis2 placement, the transformation is applied, after the derivation, to the derived attributes p defining the placement coordinate directions. For a transformed surface, the direction of the surface normal at any point is obtained by transforming the normal, at the corresponding point, to the original surface. For geometric entities with attributes (such as the radius of a circle) which have the dimensionality of length, the values will be multiplied by S.

For curves on surface the p curve.reference to curve will be unaffected by any transformation. The Cartesian transformation operator shall only be applied to geometry defined in a consistent system of units with the same units on each axis. With all optional attributes omitted, the transformation defaults to the identity transformation. The Cartesian transformation operator shall only be instantiated as one of its subtypes.

NOTE: Corresponding STEP entity : cartesian_transformation_operator, please refer to ISO/IS 10303-42:1994, p. 32 for the final definition of the formal standard.

HISTORY: New entity in IFC Release 2x.

Attribute definitions

#	Attribute	Type	Cardinality	Description	A
1	Axis1	-		This attribute is out of scope for this model view definition and shall not be set.
2	Axis2	-		This attribute is out of scope for this model view definition and shall not be set.
3	LocalOrigin	IfcCartesianPoint	[1:1]	The required translation, specified as a cartesian point. The actual translation included in the transformation is from the geometric origin to the local origin.	X
4	Scale	-		This attribute is out of scope for this model view definition and shall not be set.
	Scl :=NVL(Scale, 1.0)	REAL	[1:1]	The derived scale S of the transformation, equal to scale if that exists, or 1.0 otherwise.	X
	Dim :=LocalOrigin.Dim	IfcDimensionCount	[1:1]	The space dimensionality of this class, determined by the space dimensionality of the local origin.	X

Formal Propositions

Rule	Description
WR1	The derived scaling Scl shall be greater than zero.

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	A
IfcRepresentationItem
IfcGeometricRepresentationItem
IfcCartesianTransformationOperator
1	Axis1	-		This attribute is out of scope for this model view definition and shall not be set.
2	Axis2	-		This attribute is out of scope for this model view definition and shall not be set.
3	LocalOrigin	IfcCartesianPoint	[1:1]	The required translation, specified as a cartesian point. The actual translation included in the transformation is from the geometric origin to the local origin.	X
4	Scale	-		This attribute is out of scope for this model view definition and shall not be set.
	Scl :=NVL(Scale, 1.0)	REAL	[1:1]	The derived scale S of the transformation, equal to scale if that exists, or 1.0 otherwise.	X
	Dim :=LocalOrigin.Dim	IfcDimensionCount	[1:1]	The space dimensionality of this class, determined by the space dimensionality of the local origin.	X

Formal representations

XSD Specification

 <xs:element name="IfcCartesianTransformationOperator" type="ifc:IfcCartesianTransformationOperator" abstract="true" substitutionGroup="ifc:IfcGeometricRepresentationItem" nillable="true"/>

 <xs:complexType name="IfcCartesianTransformationOperator" abstract="true">

  <xs:complexContent>

   <xs:extension base="ifc:IfcGeometricRepresentationItem">

    <xs:sequence>

     <xs:element name="LocalOrigin" type="ifc:IfcCartesianPoint" nillable="true"/>

    </xs:sequence>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcCartesianTransformationOperator

 ABSTRACT SUPERTYPE OF(ONEOF(IfcCartesianTransformationOperator2D, IfcCartesianTransformationOperator3D))

 SUBTYPE OF (IfcGeometricRepresentationItem);

  Axis1 : OPTIONAL IfcStrippedOptional;

  Axis2 : OPTIONAL IfcStrippedOptional;

  LocalOrigin : IfcCartesianPoint;

  Scale : OPTIONAL IfcStrippedOptional;

 DERIVE

  Scl : REAL := NVL(Scale, 1.0);

  Dim : IfcDimensionCount := LocalOrigin.Dim;

 WHERE

  WR1 : Scl > 0.0;
END_ENTITY;

 EXPRESS-G diagram