IFC 4.3.x development

8.9.3.28 IfcCurveBoundedSurface

Change log

IFC4

added

8.9.3.28.1 Semantic definitions at the entity

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.

NOTE  Some surfaces, like IfcCylindricalSurface does not have identifiable implicit boundaries.

NOTE  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.

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

HISTORY  New entity in IFC4.

Informal Propositions:

  1. Each curve in the set of Boundaries shall be closed.
  2. No two curves in the set of Boundaries shall intersect.
  3. 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.

8.9.3.28.1 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
IfcSurface
Dim INVALID The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item.

> IFC4 CHANGE Derived attribute promoted from subtypes.
IfcBoundedSurface
IfcCurveBoundedSurface
1 BasisSurface IfcSurface The surface to be bounded.
2 Boundaries SET [1:?] OF IfcBoundaryCurve The outer boundary of the surface.
3 ImplicitOuter IfcBoolean

8.9.3.28.2 Entity inheritance

dot_inheritance IfcCurveBoundedSurface IfcCurveBoundedSurface IfcBoundedSurface IfcBoundedSurface IfcCurveBoundedSurface->IfcBoundedSurface IfcBoundedSurface_children 3 more... IfcBoundedSurface_children->IfcBoundedSurface IfcSurface IfcSurface IfcBoundedSurface->IfcSurface IfcSurface_children 3 more... IfcSurface_children->IfcSurface IfcGeometricRepresentationItem IfcGeometricRepresentationItem IfcSurface->IfcGeometricRepresentationItem IfcGeometricRepresentationItem_children 24 more... IfcGeometricRepresentationItem_children->IfcGeometricRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcGeometricRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem

8.9.3.28.3 Formal representations

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