IFC 4.3.x development

8.9.3.69 IfcSurfaceCurve

Change log

IFC4

added

IFC4X1

modificationswhere_rules CurveIsNotPcurve definitionChanged from not('ifc4.ifcpcurve' in typeof(Curve3D)) to not('ifc4x1.ifcpcurve' in typeof(Curve3D))

IFC4X2

modificationswhere_rules CurveIsNotPcurve definitionChanged from not('ifc4x1.ifcpcurve' in typeof(Curve3D)) to not('ifc4x2.ifcpcurve' in typeof(Curve3D))

IFC4X3_RC3

modificationswhere_rules CurveIsNotPcurve definitionChanged from not('ifc4x2.ifcpcurve' in typeof(Curve3D)) to not('ifc4x3_rc3.ifcpcurve' in typeof(Curve3D))

8.9.3.69.1 Semantic definitions at the entity

An IfcSurfaceCurve is a 3-dimensional curve that has additional representations provided by one or two pcurves.

NOTE  Definition according to ISO/CD 10303-42:1992
A surface curve is a type of curve, that is a curve on a surface. The curve is represented as a curve (curve_3d) in three-dimensional space and possibly as a curve, corresponding to a pcurve, in the two-dimensional parametric space of a surface. The ability of this curve to reference a list of 1 or 2 pcurves enables this entity to define either a curve on a single surface, or an intersection curve which has two distinct surface associations. A `seam' on a closed surface can also be represented by this entity; in this case each associated_geometry will be a pcurve lying on the same surface. Each pcurve shall be parametrised to have the same sense as curve_3d. The surface curve takes its parametrisation directly from either curve_3d or pcurve as indicated by the attribute master representation.

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

HISTORY  New entity in IFC4 Add2.

Informal Propositions:

  1. Where Curve3D and one or two pcurves exist they shall represent the same mathematical point set. (i.e., they shall coincide geometrically but may differ in parametrisation.)
  2. The Curve3D and any associated pcurves shall agree with respect to their senses.

8.9.3.69.1 Attributes

# Attribute Type Description
IfcRepresentationItem
LayerAssignment SET [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.
IfcSurfaceCurve
1 Curve3D IfcCurve The curve which is the three-dimensional representation of the surface curve.
2 AssociatedGeometry LIST [1:2] OF IfcPcurve A list of one or two pcurves which define the surface or surfaces associated with the surface curve. Two elements in this list indicate that the curve has two surface associations which need not be two distinct surfaces. Being a pcurve, it also associates a basis curve in the parameter space of this surface as an alternative representation of the surface curve.
3 MasterRepresentationIfcPreferredSurfaceCurveRepresentation The
The master_representation takes one of the values Curve3D, PCurveS1_ or PCurveS2_ to indicate a preference for the 3D curve, or the first or second pcurve, in the associated geometry list, respectively. Multiple representations provide the ability to communicate data in more than one form, even though the data is expected to be geometrically identical.



>NOTE  The master representation attribute acknowledges the impracticality of ensuring that multiple forms are indeed identical and allows the indication of a preferred form. This would probably be determined by the creator of the data. All characteristics, such as parametrisation, domain, and results of evaluation, for an entity having multiple representations, are derived from the master representation. Any use of the other representations is a compromise for practical considerations.
BasisSurface INVALID The surface, or surfaces on which the IfcSurfaceCurve lies. This is determined from the AssociatedGeometry list.

8.9.3.69.2 Entity inheritance

dot_inheritance IfcIntersectionCurve IfcIntersectionCurve IfcSurfaceCurve IfcSurfaceCurve IfcIntersectionCurve->IfcSurfaceCurve IfcCurve IfcCurve IfcSurfaceCurve->IfcCurve IfcSeamCurve IfcSeamCurve IfcSeamCurve->IfcSurfaceCurve 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

8.9.3.69.3 Formal representations

ENTITY IfcSurfaceCurve
 SUPERTYPE OF (ONEOF
	(IfcIntersectionCurve
	,IfcSeamCurve))
 SUBTYPE OF (IfcCurve);
	Curve3D : IfcCurve;
	AssociatedGeometry : LIST [1:2] OF IfcPcurve;
	MasterRepresentation : IfcPreferredSurfaceCurveRepresentation;
 DERIVE
	BasisSurface : SET [1:2] OF IfcSurface := IfcGetBasisSurface(SELF);
 WHERE
	CurveIs3D : Curve3D.Dim = 3;
	CurveIsNotPcurve : NOT ('IFC4X3_DEV.IFCPCURVE' IN TYPEOF(Curve3D));
END_ENTITY;