IfcRationalBSplineCurveWithKnots

Semantic definitions at the entity

Entity definition

A rational B-spline curve with knots is a B-spline curve described in terms of control points and basic functions. It describes weights in addition to the control points defined at the supertype IfcBSplineCurve.

All weights shall be positive and the curve is given by:

where

k+1	number of control points
P_i	control points
w_i	weights
d	degree

NOTE Entity adapted from rational_b_spline_curve in ISO 10303-42.

HISTORY New entity in IFC4.

Attribute definitions

#	Attribute	Type	Cardinality	Description	G
9	WeightsData	IfcReal	L[2:?]	The supplied values of the weights.	X
	Weights :=IfcListToArray(WeightsData,0,SELF\IfcBSplineCurve.UpperIndexOnControlPoints)	IfcReal	A[0:UpperIndexOnControlPoints]	The array of weights associated with the control points. This is derived from the weights data.	X

Formal Propositions

Rule	Description
SameNumOfWeightsAndPoints	There shall be the same number of weights as control points.
WeightsGreaterZero	All the weights shall have values greater than 0.0.

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
IfcCurve
	Dim :=IfcCurveDim(SELF)	IfcDimensionCount		The space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve.	X
IfcBoundedCurve
IfcBSplineCurve
1	Degree	IfcInteger		The algebraic degree of the basis functions.	X
2	ControlPointsList	IfcCartesianPoint	L[2:?]	The list of control points for the curve.	X
3	CurveForm	IfcBSplineCurveForm		Used to identify particular types of curve; it is for information only.	X
4	ClosedCurve	IfcLogical		Indication of whether the curve is closed; it is for information only.	X
5	SelfIntersect	IfcLogical		Indication whether the curve self-intersects or not; it is for information only.	X
	UpperIndexOnControlPoints :=(SIZEOF(ControlPointsList) - 1)	IfcInteger		The upper index on the array of control points; the lower index is 0. This value is derived from the control points list.	X
	ControlPoints :=IfcListToArray(ControlPointsList,0,UpperIndexOnControlPoints)	IfcCartesianPoint	A[0:UpperIndexOnControlPoints]	The array of control points used to define the geometry of the curve. This is derived from the list of control points.	X
IfcBSplineCurveWithKnots
6	KnotMultiplicities	IfcInteger	L[2:?]	The multiplicities of the knots. This list defines the number of times each knot in the knots list is to be repeated in constructing the knot array.	X
7	Knots	IfcParameterValue	L[2:?]	The list of distinct knots used to define the B-spline basis functions.	X
8	KnotSpec	IfcKnotType		The description of the knot type. This is for information only.	X
	UpperIndexOnKnots :=SIZEOF(Knots)	IfcInteger		The upper index on the knot arrays; the lower index is 1.	X
IfcRationalBSplineCurveWithKnots
9	WeightsData	IfcReal	L[2:?]	The supplied values of the weights.	X
	Weights :=IfcListToArray(WeightsData,0,SELF\IfcBSplineCurve.UpperIndexOnControlPoints)	IfcReal	A[0:UpperIndexOnControlPoints]	The array of weights associated with the control points. This is derived from the weights data.	X

Formal representations

XML Specification

 <xs:element name="IfcRationalBSplineCurveWithKnots" type="ifc:IfcRationalBSplineCurveWithKnots" substitutionGroup="ifc:IfcBSplineCurveWithKnots" nillable="true"/>

 <xs:complexType name="IfcRationalBSplineCurveWithKnots">

  <xs:complexContent>

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

    <xs:attribute name="WeightsData" use="optional">

     <xs:simpleType>

      <xs:restriction>

       <xs:simpleType>

        <xs:list itemType="ifc:IfcReal"/>

       </xs:simpleType>

       <xs:minLength value="2"/>

      </xs:restriction>

     </xs:simpleType>

    </xs:attribute>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcRationalBSplineCurveWithKnots

 SUBTYPE OF (IfcBSplineCurveWithKnots);

  WeightsData : LIST [2:?] OF IfcReal;

 DERIVE

  Weights : ARRAY [0:UpperIndexOnControlPoints] OF IfcReal := IfcListToArray(WeightsData,0,SELF\IfcBSplineCurve.UpperIndexOnControlPoints);

 WHERE

  SameNumOfWeightsAndPoints : SIZEOF(WeightsData) = SIZEOF(SELF\IfcBSplineCurve.ControlPointsList);
  WeightsGreaterZero : IfcCurveWeightsPositive(SELF);
END_ENTITY;

 EXPRESS-G diagram

Item	Change	Description
IFC2x3 to IFC4 4.0.0.0
IfcRationalBSplineCurveWithKnots	ADDED
IFC4 Addendum 1 4.0.1.0
IfcRationalBSplineCurveWithKnots
Degree	MODIFIED	Type changed from INTEGER to IfcInteger.
ClosedCurve	MODIFIED	Type changed from LOGICAL to IfcLogical.
SelfIntersect	MODIFIED	Type changed from LOGICAL to IfcLogical.
KnotMultiplicities	MODIFIED	Type changed from INTEGER to IfcInteger.
WeightsData	MODIFIED	Type changed from REAL to IfcReal.
IFC4x2 Candidate 4.2.0.0
IfcRationalBSplineCurveWithKnots
PositioningElement	ADDED
IFC4x2 to IFC4x3_RC1
IfcRationalBSplineCurveWithKnots
PositioningElement	MODIFIED	Aggregation changed from NONE to SET.
IFC4x3_RC2 to IFC4x3_RC3
IfcRationalBSplineCurveWithKnots
PositioningElement	DELETED

	Rationale Bézier-Spline - Kurve mit Kontrollpunkten
	Rational BSpline Curve With Knots
	Courbes Bsplines rationnelles avec nœuds