IFC 4.3.x development

8.9.3.41 IfcOffsetCurve2D

Change log

IFC4

additions where_rules DimIs2D
deletions where_rules WR1
modificationsattributes SelfIntersect definitionChanged from logical to IfcLogical

IFC4X1

deletions attributesBasisCurve
modificationssupertype Changed from IfcCurve to IfcOffsetCurve

8.9.3.41.1 Semantic definitions at the entity

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: 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.

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

HISTORY  New entity in IFC2x

8.9.3.41.1 Attributes

# Attribute Type Description
IfcRepresentationItem
LayerAssignmentSET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItemsAssignment 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.
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.



> IFC2x3 CHANGE  The inverse attribute StyledByItem has been added.
IfcGeometricRepresentationItem
IfcCurve
Dim INVALID The space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve.
IfcOffsetCurve
1 BasisCurve IfcCurve The curve that is being offset.
IfcOffsetCurve2D
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.

8.9.3.41.2 Entity inheritance

dot_inheritance IfcOffsetCurve2D IfcOffsetCurve2D IfcOffsetCurve IfcOffsetCurve IfcOffsetCurve2D->IfcOffsetCurve IfcOffsetCurve3D IfcOffsetCurve3D IfcOffsetCurve3D->IfcOffsetCurve IfcCurve IfcCurve IfcOffsetCurve->IfcCurve IfcOffsetCurveByDistances IfcOffsetCurveByDistances IfcOffsetCurveByDistances->IfcOffsetCurve IfcCurve_children 7 more... IfcCurve_children->IfcCurve IfcGeometricRepresentationItem IfcGeometricRepresentationItem IfcCurve->IfcGeometricRepresentationItem IfcGeometricRepresentationItem_children 24 more... IfcGeometricRepresentationItem_children->IfcGeometricRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcGeometricRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem

8.9.3.41.3 Formal representations

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