additions | where_rules | DimIs2D |

deletions | where_rules | WR1 |

modifications | attributes SelfIntersect definition | Changed from logical to IfcLogical |

deletions | attributes | BasisCurve |

modifications | supertype | Changed from IfcCurve to IfcOffsetCurve |

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 directionV x TwhereVis the fixed reference direction andTis the unit tangent to the basis curve. For the offset direction to be well defined,Tshall not at any point of the curve be in the same, or opposite, direction asV.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:

Tis the unit tangent vector to the basis curveC(u) at parameter valueu, anddis distance. The underlying curve shall be three-dimensional.NOTE Entity adapted from

offset_curve_3ddefined in ISO 10303-42HISTORY 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 | Type | Description |
---|---|---|---|

IfcRepresentationItem | |||

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. > 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. |

IfcOffsetCurve3D | |||

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. |

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