# 8.9.3.27 IfcCurveBoundedSurface

## 8.9.3.27.1 Semantic definition

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.

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.

## 8.9.3.27.4 Formal representation

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