8.9.3.59 IfcSeamCurve

8.9.3.59.1 Semantic definition

An IfcSeamCurve is a 3-dimensional curve that has additional representations provided by exactly two distinct pcurves describing the same curve at the two extreme ends of a closed parametric surface.

Figure 8.9.3.59.A shows an instance diagram explaining the use of IfcSeamCurve as a boundary curve of an IfcCylindricalSurface.

seam curve usage — Figure 8.9.3.59.A — use of a seam curve bounding a cylindrical surface

8.9.3.59.2 Entity inheritance

8.9.3.59.3 Attributes

#	Attribute	Type	Description
IfcRepresentationItem (2)
	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.
IfcCurve (1)
*	Dim	IfcDimensionCount	This attribute is formally derived. `IfcCurveDim(SELF)` The space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve.
Click to show 3 hidden inherited attributes
IfcSurfaceCurve (4)
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	MasterRepresentation	IfcPreferredSurfaceCurveRepresentation	The <em<MasterRepresentation defines the curve used to determine the unique parametrisation of the IfcSurfaceCurve. The master_representation takes one of the values Curve3D, PCurve_S1 or PCurve_S2 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	SET [1:2] OF IfcSurface	This attribute is formally derived. `IfcGetBasisSurface(SELF)` The surface, or surfaces on which the IfcSurfaceCurve lies. This is determined from the AssociatedGeometry list.

Table 8.9.3.59.B

8.9.3.59.4 Formal propositions

Name	Description
SameSurface	The two associated geometries shall be related to the same surface.
`IfcAssociatedSurface(SELF\IfcSurfaceCurve.AssociatedGeometry[1]) = IfcAssociatedSurface(SELF\IfcSurfaceCurve.AssociatedGeometry[2])`
TwoPCurves	The intersection curve shall have precisely two associated geometry elements.
`SIZEOF(SELF\IfcSurfaceCurve.AssociatedGeometry) = 2`

Table 8.9.3.59.C

8.9.3.59.5 Formal representation

 ENTITY IfcSeamCurve
 SUBTYPE OF (IfcSurfaceCurve);
 WHERE
	SameSurface : IfcAssociatedSurface(SELF\IfcSurfaceCurve.AssociatedGeometry[1]) = IfcAssociatedSurface(SELF\IfcSurfaceCurve.AssociatedGeometry[2]);
	TwoPCurves : SIZEOF(SELF\IfcSurfaceCurve.AssociatedGeometry) = 2;
END_ENTITY;

8.9.3.59.6 References

IfcSurfaceCurve