IFC 4.3.x development

8.9.3.60 IfcSeamCurve

Change log

IFC4

added

8.9.3.60.1 Semantic definitions at the entity

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.

NOTE&bbsp The `seam' on a cylinder has representations as the lines u = 0 or u = 360 degrees in parameter space.

Figure 1 shows an instance diagram explaining the use of IfcSeamCurve as a boundary curve of an IfcCylindricalSurface.

"seam curve usage"

NOTE  Definition according to ISO/CD 10303-42:1992
A seam curve is a type of surface curve, that is a curve on a closed parametric surface which has two distinct representations as constant parameter curves at the two extremes of the parameter range for the surface.

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

HISTORY  New entity in IFC4 Add2.

Formal Propositions

TwoPCurves

The intersection curve shall have precisely two associated geometry elements.

SameSurface

The two associated geometries shall be related to the same surface.

# 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.

8.9.3.60.1 Entity inheritance

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

8.9.3.60.2 Formal representations

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