IfcBSplineSurfaceWithKnots

ifcbsprinesSurfaceWithKnots是有理或多项式参数曲面的一种一般形式，其中节点值是直接给定的。

注：定义根据ISO/CD 10303-42:1992

这是一个B样条曲面，其中明确给出了节点值。该子类型应用于表示非均匀B样条曲面，也可用于其他结类型。

除第一个和最后一个外，所有结重数应在1，…，d范围内；第一个和最后一个可能具有最大值d+1。在计算基函数时，例如重数3的结u被解释为结数组中的序列u，u，u。

注：实体根据ISO 10303-42中定义的b_样条曲面_和_节点改编。

IFC4中增加的新实体。

Attribute definitions

#	Attribute	Type	Cardinality	Description	C
8	UMultiplicities	IfcInteger	L[2:?]	The multiplicities of the knots in the u parameter direction.	X
9	VMultiplicities	IfcInteger	L[2:?]	The multiplicities of the knots in the v parameter direction.	X
10	UKnots	IfcParameterValue	L[2:?]	The list of the distinct knots in the u parameter direction.	X
11	VKnots	IfcParameterValue	L[2:?]	The list of the distinct knots in the v parameter direction.	X
12	KnotSpec	IfcKnotType	[1:1]	The description of the knot type.	X
	KnotVUpper :=SIZEOF(VKnots)	IfcInteger	[1:1]	The number of distinct knots in the v parameter direction.	X
	KnotUUpper :=SIZEOF(UKnots)	IfcInteger	[1:1]	The number of distinct knots in the u parameter direction.	X

 

 

 

 

 

 

 

 

 

 

 

 

Formal Propositions

Rule	Description
UDirectionConstraints	The function returns TRUE when the parameter constraints are verified for the u direction.
VDirectionConstraints	The function returns TRUE when the parameter constraints are verified for the v direction.
CorrespondingULists	The number of UMultiplicities shall be the same as the number of UKnots.
CorrespondingVLists	The number of VMultiplicities shall be the same as the number of VKnots.

 

 

 

 

 

 

 

 

 

#	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
IfcSurface
	Dim :=3	IfcDimensionCount	[1:1]	The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item.	X
IfcBoundedSurface
IfcBSplineSurface
1	UDegree	IfcInteger	[1:1]	Algebraic degree of basis functions in u.	X
2	VDegree	IfcInteger	[1:1]	Algebraic degree of basis functions in v.	X
3	ControlPointsList	IfcCartesianPoint	L[2:?]L[2:?]	This is a list of lists of control points.	X
4	SurfaceForm	IfcBSplineSurfaceForm	[1:1]	Indicator of special surface types.	X
5	UClosed	IfcLogical	[1:1]	Indication of whether the surface is closed in the u direction; this is for information only.	X
6	VClosed	IfcLogical	[1:1]	Indication of whether the surface is closed in the v direction; this is for information only.	X
7	SelfIntersect	IfcLogical	[1:1]	Flag to indicate whether, or not, surface is self-intersecting; this is for information only.	X
	UUpper :=SIZEOF(ControlPointsList) - 1	IfcInteger	[1:1]	Upper index on control points in u direction.	X
	VUpper :=SIZEOF(ControlPointsList[1]) - 1	IfcInteger	[1:1]	Upper index on control points in v direction.	X
	ControlPoints :=IfcMakeArrayOfArray(ControlPointsList, 0,UUpper,0,VUpper)	IfcCartesianPoint	A[0:UUpper]A[0:VUpper]	Array (two-dimensional) of control points defining surface geometry. This array is constructed from the control points list.	X
IfcBSplineSurfaceWithKnots
8	UMultiplicities	IfcInteger	L[2:?]	The multiplicities of the knots in the u parameter direction.	X
9	VMultiplicities	IfcInteger	L[2:?]	The multiplicities of the knots in the v parameter direction.	X
10	UKnots	IfcParameterValue	L[2:?]	The list of the distinct knots in the u parameter direction.	X
11	VKnots	IfcParameterValue	L[2:?]	The list of the distinct knots in the v parameter direction.	X
12	KnotSpec	IfcKnotType	[1:1]	The description of the knot type.	X
	KnotVUpper :=SIZEOF(VKnots)	IfcInteger	[1:1]	The number of distinct knots in the v parameter direction.	X
	KnotUUpper :=SIZEOF(UKnots)	IfcInteger	[1:1]	The number of distinct knots in the u parameter direction.	X

 

EXPRESS Specification

ENTITY IfcBSplineSurfaceWithKnots
 SUPERTYPE OF(IfcRationalBSplineSurfaceWithKnots)
 SUBTYPE OF (IfcBSplineSurface);
  UMultiplicities : LIST [2:?] OF IfcInteger;
  VMultiplicities : LIST [2:?] OF IfcInteger;
  UKnots : LIST [2:?] OF IfcParameterValue;
  VKnots : LIST [2:?] OF IfcParameterValue;
  KnotSpec : IfcKnotType;
 DERIVE
  KnotVUpper : IfcInteger := SIZEOF(VKnots);
  KnotUUpper : IfcInteger := SIZEOF(UKnots);
 WHERE
  UDirectionConstraints : IfcConstraintsParamBSpline ( SELF\IfcBSplineSurface.UDegree, KnotUUpper, SELF\IfcBSplineSurface.UUpper, UMultiplicities, UKnots);
  VDirectionConstraints : IfcConstraintsParamBSpline ( SELF\IfcBSplineSurface.VDegree, KnotVUpper, SELF\IfcBSplineSurface.VUpper, VMultiplicities, VKnots);
  CorrespondingULists : SIZEOF(UMultiplicities) = KnotUUpper;
  CorrespondingVLists : SIZEOF(VMultiplicities) = KnotVUpper;
END_ENTITY;