added |

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

IfcCylindricalSurfacedoes 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 offrom any point on the boundary, whereNxTNis the surface normal andTthe boundary curve tangent vector at this point. The region so defined shall be arcwise connected.NOTE Entity adapted from

curve_bounded_surfacedefined in ISO 10303-42.HISTORY 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.

# | Attribute | Type | Description |
---|---|---|---|

IfcRepresentationItem | |||

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. | |

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 |

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