8.9.3.27 IfcCurveBoundedSurface

The IfcCurveBoundedSurface is a parametric surface with boundaries defined by p-curves, that is, a curve which lies on the basis of a surface and is defined in the parameter space of that surface. The p-curve is a special type of a composite curve segment and shall only be used to bound a surface.

The outer boundary shall be either defined by:

an IfcOuterBoundaryCurve a closed composite curve on surface for the definition of an outer boundary, in this case the attribute ImplicitOuter has to be set to FALSE, or
an implicit boundary of the bounded surface, e.g. the u1, u2, v1, v2 of IfcRectangularTrimmedSurface, in this case the attribute ImplicitOuter has to be set to TRUE.

Some surfaces, like IfcCylindricalSurface does not have identifiable implicit boundaries. Definition according to ISO/CD 10303-42:1992 The curve bounded surface is a parametric surface with curved boundaries defined by one or more boundary curves. One of the boundary curves may be the outer boundary; any number of inner boundaries is permissible. The region of the curve bounded surface in the basis surface is defined to be the portion of the basis surface in the direction of N x T from any point on the boundary, where N is the surface normal and T the boundary curve tangent vector at this point. The region so defined shall be arcwise connected. Entity adapted from curve_bounded_surface defined in ISO 10303-42. New entity in IFC4.

Informal Propositions

Each curve in the set of Boundaries shall be closed.
No two curves in the set of Boundaries shall intersect.
At most one of the boundary curves may enclose any other boundary curve. If an IfcOuterBoundaryCurve is designated, only that curve may enclose any other boundary curve.

8.9.3.27.2 Entity inheritance

8.9.3.27.3 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.
IfcSurface (1)
*	Dim	IfcDimensionCount	This attribute is formally derived. `3` The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item. IFC4-CHANGE Derived attribute promoted from subtypes.
Click to show 3 hidden inherited attributes Click to hide 3 inherited attributes
IfcCurveBoundedSurface (3)
1	BasisSurface	IfcSurface	The surface to be bounded.
2	Boundaries	SET [1:?] OF IfcBoundaryCurve	The outer boundary of the surface.
3	ImplicitOuter	IfcBoolean	No description available.

Table 8.9.3.27.A

8.9.3.27.4 Formal representation

ENTITY IfcCurveBoundedSurface
 SUBTYPE OF (IfcBoundedSurface);
	BasisSurface : IfcSurface;
	Boundaries : SET [1:?] OF IfcBoundaryCurve;
	ImplicitOuter : IfcBoolean;
END_ENTITY;

8.9.3.27.5 References

IfcBoundedSurface

8.9.3.27 IfcCurveBoundedSurface

8.9.3.27.1 Semantic definition

8.9.3.27.2 Entity inheritance

8.9.3.27.3 Attributes

8.9.3.27.4 Formal representation

8.9.3.27.5 References

8.9.3.27.6 Changelog

8.9.3.27.6.1 IFC4