IfcCompositeCurveOnSurface

IfcCompositeCurveOnSurface是基于p曲线的线段集合。i、 e.以曲面为基础并在该曲面的参数空间中定义的曲线。p-曲线段是复合曲线段的一种特殊类型，仅用于绑定曲面。

注：定义根据ISO/CD 10303-42:1992

复合面上线是曲面上曲线的线段的集合。每段应位于基面上。

相邻节段之间至少应有位置连续性。组合曲线的参数化是通过分段参数范围的累积得到的。第一段从0参数化到l1，对于i≥2，第i段参数化自

式中，lk是第k条曲线段的参数长度（即最大和最小参数值之间的差值）。

实体改编自ISO 10303-42中定义的曲面上的复合曲线。

IFC4中增加的新实体。

Formal Propositions

Rule	Description
SameSurface	The BasisSurface shall contain at least one surface (and exactly one surface). This ensures that all segments reference curves on the same surface.

#	Attribute	Type	Cardinality	Description	C
IfcRepresentationItem
	LayerAssignment	IfcPresentationLayerAssignment @AssignedItems	S[0:1]	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.	X
	StyledByItem	IfcStyledItem @Item	S[0:1]	Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve.	X
IfcGeometricRepresentationItem
IfcCurve
	Dim :=IfcCurveDim(SELF)	IfcDimensionCount	[1:1]	The space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve.	X
IfcBoundedCurve
IfcCompositeCurve
1	Segments	IfcCompositeCurveSegment	L[1:?]	The component bounded curves, their transitions and senses. The transition attribute for the last segment defines the transition between the end of the last segment and the start of the first; this transition attribute may take the value discontinuous, which indicates an open curve.	X
2	SelfIntersect	IfcLogical	[1:1]	Indication of whether the curve intersects itself or not; this is for information only.	X
	NSegments :=SIZEOF(Segments)	IfcInteger	[1:1]	The number of component curves.	X
	ClosedCurve :=Segments[NSegments].Transition <> Discontinuous	IfcLogical	[1:1]	Indication whether the curve is closed or not; this is derived from the transition code of the last segment.	X
IfcCompositeCurveOnSurface
	BasisSurface :=IfcGetBasisSurface(SELF)	IfcSurface	S[0:1]	The surface on which the composite curve is defined.	X

EXPRESS Specification

ENTITY IfcCompositeCurveOnSurface
 SUPERTYPE OF(IfcBoundaryCurve)
 SUBTYPE OF (IfcCompositeCurve);
 DERIVE
  BasisSurface : SET [0:1] OF IfcSurface := IfcGetBasisSurface(SELF);
 WHERE
  SameSurface : SIZEOF(BasisSurface) > 0;
END_ENTITY;