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 *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

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

offset_curve_2ddefined in ISO 10303-42.HISTORY New entity in IFC2x

# | 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. |

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. |

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