IfcBSplineSurface

IfcBSplineSurface是有理或多项式参数曲面的一般形式。

b_样条曲面是有理或多项式参数曲面的一般形式，它由控制点、基函数和可能的权重来表示。与相应的曲线实体一样，它有一些特殊的子类型，其中一些数据可以从中派生出来。

The symbology used here is:

K1	= upper_index_on_u_control_points
K2	= upper_index_on_v_control_points
Pij	= control_points
wij	= weights
d1	= u_degree
d2	= v_degree

#	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