IFC 4.3.0.0 (IFC4X3) final

8.9.3.41 IfcOffsetCurve2D

8.9.3.41.1 Semantic definition

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

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: Math 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.
Figure 8.9.3.41.A

8.9.3.41.2 Entity inheritance

8.9.3.41.3 Attributes

# Attribute Type Description
IfcRepresentationItem (2)
LayerAssignment SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems

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.
StyledByItem SET [0:1] OF IfcStyledItem FOR Item

Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve.
IfcCurve (1)
* Dim IfcDimensionCount

This attribute is formally derived. 

IfcCurveDim(SELF)

The space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve.
IfcOffsetCurve (1)
1 BasisCurve IfcCurve

The curve that is being offset.
Click to show 4 hidden inherited attributes Click to hide 4 inherited attributes
IfcOffsetCurve2D (2)
2 Distance IfcLengthMeasure

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).)
3 SelfIntersect IfcLogical

An indication of whether the offset curve self-intersects; this is for information only.
Table 8.9.3.41.B

8.9.3.41.4 Formal propositions

Name Description
DimIs2D

The underlying curve shall be defined in two-dimensional space.

 
BasisCurve.Dim = 2
Table 8.9.3.41.C

8.9.3.41.5 Formal representation 

ENTITY IfcOffsetCurve2D
 SUBTYPE OF (IfcOffsetCurve);
	Distance : IfcLengthMeasure;
	SelfIntersect : IfcLogical;
 WHERE
	DimIs2D : BasisCurve.Dim = 2;
END_ENTITY;

8.9.3.41.6 Changelog

  • where_rules, DimIs2D
  • where_rules, WR1
  • attributes SelfIntersect definition, Changed from logical to IfcLogical