added |

additions | where_rules | DirectrixBounded |

deletions | where_rules | DirectrixBounded |

additions | where_rules | DirectrixBounded |

deletions | where_rules | DirectrixBounded |

deletions | attributes | Directrix |

deletions | attributes | EndParam |

deletions | attributes | StartParam |

deletions | where_rules | DirectrixBounded |

modifications | supertype | Changed from IfcSweptAreaSolid to IfcDirectrixCurveSweptAreaSolid |

An *IfcFixedReferenceSweptAreaSolid* is a type of swept area solid which is the result of sweeping an area along a *Directrix*. The swept area is provided by a subtype of *IfcProfileDef*. The profile is placed by an implicit cartesian transformation operator at the start point of the sweep, where the profile normal agrees to the start tangent of the directrix at this point, and the profile's x-axis agrees to the orthogonal projection of the *FixedReference* direction within the plane of start tangent and *Fixed_Reference*. The orientation of the curve during the sweeping operation is controlled by the *FixedReference* direction.

The *SweptArea* is swept along the *Directrix* in such a way that the origin of the local coordinate system used to define the *SweptArea* is on the *Directrix* and the local x-axis is in the direction of the projection of *FixedReference* onto the normal plane to the directrix at this point. The resulting solid has the property that the cross section of the surface by the normal plane to the *Directrix* at any point is a copy of the *SweptArea*. The resulting swept solid is placed by the *Position* coordinate system.

The *Directrix* and the *ReferenceSurface* are positioned within the object coordinate system. The start of the sweeping operation is at the *StartParam*, being either the parameter value based on the curve parameterization, or by a length measured along the directrix from its beginning. If no *StartParam* is provided the start defaults to the begin of the directrix. The end of the sweeping operation is at the *EndParam*, being either the parameter value based on the curve parameterization, or by a length measured along the directrix from its beginning. If no *EndParam* is provided the end defaults to the end of the directrix.

NOTE The

StartParamand theEndParam, if provided as a parameter value, are not normalized by default, they depend upon the parameterization of the curve. However using theIfcReparametrisedCompositeCurveSegmentwithin anIfcCompositeCurveas the directrix allows to explicitly reparameterize the underlying sweeping curve.NOTE In the case of a curve composed of

IfcCurveSegment, theIfcSweptAreaSolidPositionis dependent on theIfcCurveSegmentStartPlacementand the type ofBasisCurvewhich defines thename-functionbetween the start and end (explicitly defined as the start point of the next segment) points of the segmentEXAMPLE The reference surface is any surface (plane, cylindric, composite) situated in 3D space and positioned in the object coordinate system. In many cases, it is a surface of extrusion. The directrix lies on the surface, often defined as a p-curve at this reference surface. At any point of the directrix, a plane can be constructed. The origin of the position coordinate system lies at the directrix. The Axis3 (the z-axis, or normal) of the position coordinate system is identical to the tangent of the directrix at this point, the Axis1 (the x axis, or u) of the position coordinate system is identical to the

FixedReferencedirection. The Axis2 (the y axis, or v) is constructed. In this case the resulting swept solid is not repositioned.

The orientation of the *SweptArea* as it sweeps along the *Directrix* is precisely defined by a *CartesianTransformationOperator3d* with attributes:

*LocalOrigin*as point (0; 0; 0),*Axis1*as the orthogonal projection of the*FixedReference*onto the normal plane defined by*Axis3*.*Axis3*as the direction of the tangent vector**t**at the point of the*Directrix*with parameter**u**.

The remaining attributes are defaulted to define a corresponding transformation matrix **T(u)**, which varies with the *Directrix* parameter **u**.

NOTE The geometric shape of the solid is not dependent upon the curve parameterization; the volume depends upon the area swept and the length of the

Directrix.NOTE Entity adapted from

fixed_reference_swept_surfacedefined in ISO 10303-42.HISTORY New entity in IFC4.

Informal Propositions:

- The
*SweptArea*shall lie in the plane z = 0. - The
*FixedReference*shall not be parallel to a tangent vector to the directrix at any point along this curve. - The
*Directrix*curve shall be tangent continuous.

# | 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 | |||

IfcSolidModel | |||

Dim | INVALID | The space dimensionality of this class, it is always 3. | |

IfcSweptAreaSolid | |||

1 | SweptArea | IfcProfileDef | The surface defining the area to be swept. It is given as a profile definition within the xy plane of the position coordinate system. |

2 | Position | OPTIONAL IfcAxis2Placement3D | Position coordinate system for the resulting swept solid of the sweeping operation. The position coordinate system allows for re-positioning of the swept solid. If not provided, the swept solid remains within the position as determined by the cross section or by the directrix used for the sweeping operation. > IFC4 CHANGE The attribute has been changed to OPTIONAL with upward compatibility for file-based exchange. |

IfcDirectrixCurveSweptAreaSolid | |||

3 | Directrix | IfcCurve | The curve used to define the sweeping operation. The solid is generated by sweeping the SELF\IfcSweptAreaSolid.SweptArea along the Directrix. |

4 | StartParam | OPTIONAL IfcCurveMeasureSelect | The parameter value on the Directrix at which the sweeping operation commences. If no value is provided the start of the sweeping operation is at the start of the Directrix. |

5 | EndParam | OPTIONAL IfcCurveMeasureSelect | The parameter value on the Directrix at which the sweeping operation ends. If no value is provided the end of the sweeping operation is at the end of the Directrix. |

IfcFixedReferenceSweptAreaSolid | |||

6 | FixedReference | IfcDirection |

ENTITY IfcFixedReferenceSweptAreaSolid SUPERTYPE OF (ONEOF (IfcDirectrixDerivedReferenceSweptAreaSolid)) SUBTYPE OF (IfcDirectrixCurveSweptAreaSolid); FixedReference : IfcDirection; END_ENTITY;