IfcOffsetCurve2D

Semantic definitions at the entity

Entity definition

An IfcOffsetCurve2D is a curve defined by an offset in 2D space from its BasisCurve.

NOTE Definition according to ISO/CD 10303-42:1992
An offset curve 2d is a curve at a constant distance from a basis curve in two-dimensional space. This entity defines a simple plane-offset curve by offsetting by distance along the normal to basis curve in the plane of basis curve. 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.
NOTE The offset curve 2d 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 2d takes its parameterization from the basis curve. The offset curve 2d is parameterized as:

where 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 two-dimensional.

NOTE Entity adapted from offset_curve_2d defined in ISO 10303-42.

HISTORY New entity in IFC2x

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. distance may be positive, negative or zero. A positive value of distance defines an offset in the direction which is normal to the curve in the sense of an anti-clockwise rotation through 90 degrees from the tangent vector T at the given point. (This is in the direction of orthogonal complement(T).)	X
3	SelfIntersect	IfcLogical	[1:1]	An indication of whether the offset curve self-intersects; this is for information only.	X

Formal Propositions

Rule	Description
DimIs2D	The underlying curve shall be defined in two-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
IfcOffsetCurve2D
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. distance may be positive, negative or zero. A positive value of distance defines an offset in the direction which is normal to the curve in the sense of an anti-clockwise rotation through 90 degrees from the tangent vector T at the given point. (This is in the direction of orthogonal complement(T).)	X
3	SelfIntersect	IfcLogical	[1:1]	An indication of whether the offset curve self-intersects; this is for information only.	X

Formal representations

XSD Specification

 <xs:element name="IfcOffsetCurve2D" type="ifc:IfcOffsetCurve2D" substitutionGroup="ifc:IfcCurve" nillable="true"/>

 <xs:complexType name="IfcOffsetCurve2D">

  <xs:complexContent>

   <xs:extension base="ifc:IfcCurve">

    <xs:sequence>

     <xs:element name="BasisCurve" type="ifc:IfcCurve" 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 IfcOffsetCurve2D

 SUBTYPE OF (IfcCurve);

  BasisCurve : IfcCurve;

  Distance : IfcLengthMeasure;

  SelfIntersect : IfcLogical;

 WHERE

  DimIs2D : BasisCurve.Dim = 2;
END_ENTITY;

 EXPRESS-G diagram

Item	Change	Description
IFC4 Addendum 1
IfcOffsetCurve2D
SelfIntersect	MODIFIED	Type changed from LOGICAL to IfcLogical.

	Versetzte Kurve im zweidimensionalen Raum (2D)
	Offset Curve2 D
	Décalage de courbe 2D