IfcOffsetCurve3D

Semantic definitions at the entity

Entity definition

An IfcOffsetCurve3D is a curve defined by an offset in 3D space from its BasisCurve.

NOTE Definition according to ISO/CD 10303-42:1992
An offset curve 3d is a curve at a constant distance from a basis curve in three-dimensional space. The underlying curve shall have a well-defined tangent direction at every point. In the case of a composite curve the transition code between each segment shall be cont same gradient or cont same gradient same curvature. The offset curve at any point (parameter) on the basis curve is in the direction V x T where V is the fixed reference direction and T is the unit tangent to the basis curve. For the offset direction to be well defined, T shall not at any point of the curve be in the same, or opposite, direction as V.
NOTE The offset curve 3d may differ in nature from the basis curve; the offset of a non self- intersecting curve can be self-intersecting. Care should be taken to ensure that the offset to a continuous curve does not become discontinuous.
The offset curve 3d takes its parameterization from the basis curve. The offset curve 3d is parameterized as:
T is the unit tangent vector to the basis curve C(u) at parameter value u, and d is distance. The underlying curve shall be three-dimensional.

NOTE Entity adapted from offset_curve_3d defined in ISO 10303-42

HISTORY New entity in IFC2x

Informal Propositions:

At no point on the curve shall ref direction be parallel, or opposite to, the direction of the tangent vector.

Attribute definitions

#	Attribute	Type	Cardinality	Description	C
1	BasisCurve	IfcCurve	[1:1]	The curve that is being offset.	X
2	Distance	IfcLengthMeasure	[1:1]	The distance of the offset curve from the basis curve. The distance may be positive, negative or zero.	X
3	SelfIntersect	IfcLogical	[1:1]	An indication of whether the offset curve self-intersects, this is for information only.	X
4	RefDirection	IfcDirection	[1:1]	The direction used to define the direction of the offset curve 3d from the basis curve.	X

Formal Propositions

Rule	Description
DimIs2D	The underlying curve shall be defined in three-dimensional space.

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	C
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.	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.	X
IfcGeometricRepresentationItem
IfcCurve
	Dim :=IfcCurveDim(SELF)	IfcDimensionCount	[1:1]	The space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve.	X
IfcOffsetCurve3D
1	BasisCurve	IfcCurve	[1:1]	The curve that is being offset.	X
2	Distance	IfcLengthMeasure	[1:1]	The distance of the offset curve from the basis curve. The distance may be positive, negative or zero.	X
3	SelfIntersect	IfcLogical	[1:1]	An indication of whether the offset curve self-intersects, this is for information only.	X
4	RefDirection	IfcDirection	[1:1]	The direction used to define the direction of the offset curve 3d from the basis curve.	X

Formal representations

XSD Specification

 <xs:element name="IfcOffsetCurve3D" type="ifc:IfcOffsetCurve3D" substitutionGroup="ifc:IfcCurve" nillable="true"/>

 <xs:complexType name="IfcOffsetCurve3D">

  <xs:complexContent>

   <xs:extension base="ifc:IfcCurve">

    <xs:sequence>

     <xs:element name="BasisCurve" type="ifc:IfcCurve" nillable="true"/>

     <xs:element name="RefDirection" type="ifc:IfcDirection" nillable="true"/>

    </xs:sequence>

    <xs:attribute name="Distance" type="ifc:IfcLengthMeasure" use="optional"/>

    <xs:attribute name="SelfIntersect" type="ifc:IfcLogical" use="optional"/>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcOffsetCurve3D

 SUBTYPE OF (IfcCurve);

  BasisCurve : IfcCurve;

  Distance : IfcLengthMeasure;

  SelfIntersect : IfcLogical;

  RefDirection : IfcDirection;

 WHERE

  DimIs2D : BasisCurve.Dim = 3;
END_ENTITY;

 EXPRESS-G diagram

Item	Change	Description
IFC4 Addendum 1
IfcOffsetCurve3D
SelfIntersect	MODIFIED	Type changed from LOGICAL to IfcLogical.

	Versetzte Kurve im dreidimensionalen Raum (3D)
	Offset Curve3 D
	Décalage de courbe 3D