IFC (IFC4X3) development IfcOffsetCurve3D Semantic definition

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

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: Math 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.

Informal Propositions:

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


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
IfcOffsetCurve3D (3)
2 Distance IfcLengthMeasure

The distance of the offset curve from the basis curve. The distance may be positive, negative or zero.

3 SelfIntersect IfcLogical

An indication of whether the offset curve self-intersects, this is for information only.

4 RefDirection IfcDirection

The direction used to define the direction of the offset curve 3d from the basis curve.

Table Formal propositions

Name Description

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

BasisCurve.Dim = 3
Table Formal representation

ENTITY IfcOffsetCurve3D
 SUBTYPE OF (IfcOffsetCurve);
	Distance : IfcLengthMeasure;
	SelfIntersect : IfcLogical;
	RefDirection : IfcDirection;
	DimIs2D : BasisCurve.Dim = 3;

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  • where rule, DimIs2D
  • where rule, WR1
  • attribute SelfIntersect type, Changed from "logical" to "IfcLogical"