IfcCartesianTransformationOperator

Semantic definitions at the entity

Entity definition

An IfcCartesianTransformationOperator defines an abstract supertype of different kinds of geometric transformations.

NOTE Definition according to 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 + _S_TP 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 Entity adapted from cartesian_transformation_operator defined in ISO10303-42.

HISTORY New entity in IFC2x.

Attribute definitions

#	Attribute	Type	Cardinality	Description	G
1	Axis1	IfcDirection	?	The direction used to determine U[1], the derived X axis direction.	X
2	Axis2	IfcDirection	?	The direction used to determine U[2], the derived Y axis direction.	X
3	LocalOrigin	IfcCartesianPoint		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	IfcReal	?	The scaling value specified for the transformation.	X
	Scl :=NVL(Scale, 1.0)	IfcReal		The derived scale S of the transformation, equal to scale if that exists, or 1.0 otherwise.	X
	Dim :=LocalOrigin.Dim	IfcDimensionCount		The space dimensionality of this class, determined by the space dimensionality of the local origin.	X

Formal Propositions

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

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	G
IfcRepresentationItem
	LayerAssignment	IfcPresentationLayerAssignment @AssignedItems	S[0:1]	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.	X
	StyledByItem	IfcStyledItem @Item	S[0:1]	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.	X
IfcGeometricRepresentationItem
IfcCartesianTransformationOperator
1	Axis1	IfcDirection	?	The direction used to determine U[1], the derived X axis direction.	X
2	Axis2	IfcDirection	?	The direction used to determine U[2], the derived Y axis direction.	X
3	LocalOrigin	IfcCartesianPoint		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	IfcReal	?	The scaling value specified for the transformation.	X
	Scl :=NVL(Scale, 1.0)	IfcReal		The derived scale S of the transformation, equal to scale if that exists, or 1.0 otherwise.	X
	Dim :=LocalOrigin.Dim	IfcDimensionCount		The space dimensionality of this class, determined by the space dimensionality of the local origin.	X

Formal representations

XML 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="Axis1" type="ifc:IfcDirection" nillable="true" minOccurs="0"/>

     <xs:element name="Axis2" type="ifc:IfcDirection" nillable="true" minOccurs="0"/>

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

    </xs:sequence>

    <xs:attribute name="Scale" type="ifc:IfcReal" use="optional"/>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcCartesianTransformationOperator

 ABSTRACT SUPERTYPE OF(ONEOF(IfcCartesianTransformationOperator2D, IfcCartesianTransformationOperator3D))

 SUBTYPE OF (IfcGeometricRepresentationItem);

  Axis1 : OPTIONAL IfcDirection;

  Axis2 : OPTIONAL IfcDirection;

  LocalOrigin : IfcCartesianPoint;

  Scale : OPTIONAL IfcReal;

 DERIVE

  Scl : IfcReal := NVL(Scale, 1.0);

  Dim : IfcDimensionCount := LocalOrigin.Dim;

 WHERE

  ScaleGreaterZero : Scl > 0.0;
END_ENTITY;

 EXPRESS-G diagram

	Kartesische Transformation
	Cartesian Transformation Operator
	Opérateur de transformation cartésienne