IFC 4.3.x development

8.8.3.19 IfcFixedReferenceSweptAreaSolid

Change log

IFC4

added

IFC4X1

additionswhere_rulesDirectrixBounded
deletionswhere_rulesDirectrixBounded

IFC4X2

additionswhere_rulesDirectrixBounded
deletionswhere_rulesDirectrixBounded

IFC4X3_RC3

deletions attributes Directrix
deletions attributes EndParam
deletions attributes StartParam
deletions where_rulesDirectrixBounded
modificationssupertype Changed from IfcSweptAreaSolid to IfcDirectrixCurveSweptAreaSolid

8.8.3.19.1 Semantic definitions at the entity

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 StartParam and the EndParam, if provided as a parameter value, are not normalized by default, they depend upon the parameterization of the curve. However using the IfcReparametrisedCompositeCurveSegment within an IfcCompositeCurve as the directrix allows to explicitly reparameterize the underlying sweeping curve.

NOTE  In the case of a curve composed of IfcCurveSegment, the IfcSweptAreaSolid Position is dependent on the IfcCurveSegment StartPlacement and the type of BasisCurve which defines the name-function between the start and end (explicitly defined as the start point of the next segment) points of the segment

EXAMPLE  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 FixedReference direction. 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_surface defined in ISO 10303-42.

HISTORY  New entity in IFC4.

Informal Propositions:

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

8.8.3.19.1 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
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

8.8.3.19.2 Entity inheritance

dot_inheritance IfcDirectrixDerivedReferenceSweptAreaSolid IfcDirectrixDerivedReferenceSweptAreaSolid IfcFixedReferenceSweptAreaSolid IfcFixedReferenceSweptAreaSolid IfcDirectrixDerivedReferenceSweptAreaSolid->IfcFixedReferenceSweptAreaSolid IfcDirectrixCurveSweptAreaSolid IfcDirectrixCurveSweptAreaSolid IfcFixedReferenceSweptAreaSolid->IfcDirectrixCurveSweptAreaSolid IfcSurfaceCurveSweptAreaSolid IfcSurfaceCurveSweptAreaSolid IfcSurfaceCurveSweptAreaSolid->IfcDirectrixCurveSweptAreaSolid IfcSweptAreaSolid IfcSweptAreaSolid IfcDirectrixCurveSweptAreaSolid->IfcSweptAreaSolid IfcExtrudedAreaSolid IfcExtrudedAreaSolid IfcExtrudedAreaSolid->IfcSweptAreaSolid IfcSolidModel IfcSolidModel IfcSweptAreaSolid->IfcSolidModel IfcRevolvedAreaSolid IfcRevolvedAreaSolid IfcRevolvedAreaSolid->IfcSweptAreaSolid IfcSolidModel_children 4 more... IfcSolidModel_children->IfcSolidModel IfcGeometricRepresentationItem IfcGeometricRepresentationItem IfcSolidModel->IfcGeometricRepresentationItem IfcGeometricRepresentationItem_children 24 more... IfcGeometricRepresentationItem_children->IfcGeometricRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcGeometricRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem

8.8.3.19.3 Formal representations

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