IfcRationalBSplineSurfaceWithKnots

Item	Change	Description
IFC2x3 to IFC4 4.0.0.0
IfcRationalBSplineSurfaceWithKnots	ADDED
IFC4 Addendum 1 4.0.1.0
IfcRationalBSplineSurfaceWithKnots
UDegree	MODIFIED	Type changed from INTEGER to IfcInteger.
VDegree	MODIFIED	Type changed from INTEGER to IfcInteger.
UClosed	MODIFIED	Type changed from LOGICAL to IfcLogical.
VClosed	MODIFIED	Type changed from LOGICAL to IfcLogical.
SelfIntersect	MODIFIED	Type changed from LOGICAL to IfcLogical.
UMultiplicities	MODIFIED	Type changed from INTEGER to IfcInteger.
VMultiplicities	MODIFIED	Type changed from INTEGER to IfcInteger.
WeightsData	MODIFIED	Type changed from REAL to IfcReal.

Semantic definitions at the entity

Entity definition

A rational B-spline surface with knots is a piecewise parametric rational surface described in terms of control points, and associated weight values.

The surface is to be interpreted as follows:

σ

NOTE Entity adapted from rational_b_spline_surface in ISO 10303-42.

HISTORY New entity in IFC4.

Attribute definitions

#	Attribute	Type	Cardinality	Description	G
13	WeightsData	IfcReal	L[2:?] L[2:?]	The weights associated with the control points in the rational case.	X
	Weights :=IfcMakeArrayOfArray(WeightsData,0,UUpper,0,VUpper)	IfcReal	A[0:UUpper] A[0:VUpper]	Array (two-dimensional) of weight values constructed from the WeightsData.	X

Formal Propositions

Rule	Description
CorrespondingWeightsDataLists	The array dimensions for the weights shall be consistent with the control points data.
WeightValuesGreaterZero	The weight value associated with each control point shall be greater than zero.

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	G
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. 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.	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. IFC2x3 CHANGE The inverse attribute StyledByItem has been added.	X
IfcGeometricRepresentationItem
IfcSurface
	Dim :=3	IfcDimensionCount		The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item. IFC4 CHANGE Derived attribute promoted from subtypes.	X
IfcBoundedSurface
IfcBSplineSurface
1	UDegree	IfcInteger		Algebraic degree of basis functions in u.	X
2	VDegree	IfcInteger		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		Indicator of special surface types.	X
5	UClosed	IfcLogical		Indication of whether the surface is closed in the u direction; this is for information only.	X
6	VClosed	IfcLogical		Indication of whether the surface is closed in the v direction; this is for information only.	X
7	SelfIntersect	IfcLogical		Flag to indicate whether, or not, surface is self-intersecting; this is for information only.	X
	UUpper :=SIZEOF(ControlPointsList) - 1	IfcInteger		Upper index on control points in u direction.	X
	VUpper :=SIZEOF(ControlPointsList[1]) - 1	IfcInteger		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		The description of the knot type.	X
	KnotVUpper :=SIZEOF(VKnots)	IfcInteger		The number of distinct knots in the v parameter direction.	X
	KnotUUpper :=SIZEOF(UKnots)	IfcInteger		The number of distinct knots in the u parameter direction.	X
IfcRationalBSplineSurfaceWithKnots
13	WeightsData	IfcReal	L[2:?] L[2:?]	The weights associated with the control points in the rational case.	X
	Weights :=IfcMakeArrayOfArray(WeightsData,0,UUpper,0,VUpper)	IfcReal	A[0:UUpper] A[0:VUpper]	Array (two-dimensional) of weight values constructed from the WeightsData.	X

Formal representations

XML Specification

 <xs:element name="IfcRationalBSplineSurfaceWithKnots" type="ifc:IfcRationalBSplineSurfaceWithKnots" substitutionGroup="ifc:IfcBSplineSurfaceWithKnots" nillable="true"/>

 <xs:complexType name="IfcRationalBSplineSurfaceWithKnots">

  <xs:complexContent>

   <xs:extension base="ifc:IfcBSplineSurfaceWithKnots">

    <xs:sequence>

     <xs:element name="WeightsData">

      <xs:complexType>

       <xs:sequence>

        <xs:element ref="ifc:IfcReal-wrapper" minOccurs="4" maxOccurs="unbounded"/>

       </xs:sequence>

       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcReal-wrapper"/>

       <xs:attribute ref="ifc:cType" fixed="list list"/>

       <xs:attribute ref="ifc:arraySize" use="optional"/>

      </xs:complexType>

     </xs:element>

    </xs:sequence>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcRationalBSplineSurfaceWithKnots

 SUBTYPE OF (IfcBSplineSurfaceWithKnots);

  WeightsData : LIST [2:?] OF LIST [2:?] OF IfcReal;

 DERIVE

  Weights : ARRAY [0:UUpper] OF ARRAY [0:VUpper] OF IfcReal := IfcMakeArrayOfArray(WeightsData,0,UUpper,0,VUpper);

 WHERE

  CorrespondingWeightsDataLists : (SIZEOF(WeightsData) = SIZEOF(SELF\IfcBSplineSurface.ControlPointsList))

AND 

(SIZEOF(WeightsData[1]) = SIZEOF(SELF\IfcBSplineSurface.ControlPointsList[1]));
  WeightValuesGreaterZero : IfcSurfaceWeightsPositive(SELF);
END_ENTITY;

 EXPRESS-G diagram

	Rationale Bézier-Spline - Oberfläche mit Kontrollpunkten
	Rational BSpline Surface With Knots
	Surfaces Bsplines rationnelles avec nœuds