IfcRationalBSplineCurveWithKnots

Natural language names
Rationale Bézier-Spline - Kurve mit Kontrollpunkten
Rational BSpline Curve With Knots
Courbes Bsplines rationnelles avec nœuds
Change log
ItemSPFXMLChangeDescription
IFC2x3 to IFC4
    IfcRationalBSplineCurveWithKnotsADDED
IFC4 Addendum 1
    IfcRationalBSplineCurveWithKnots
      DegreeMODIFIEDType changed from INTEGER to IfcInteger.
      ClosedCurveMODIFIEDType changed from LOGICAL to IfcLogical.
      SelfIntersectMODIFIEDType changed from LOGICAL to IfcLogical.
      KnotMultiplicitiesMODIFIEDType changed from INTEGER to IfcInteger.
      WeightsDataMODIFIEDType changed from REAL to IfcReal.
IFC4x2 FINAL
    IfcRationalBSplineCurveWithKnots
      PositioningElementADDED
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:

Math

where

k+1 number of control points
Pi control points
wi weights
d degree
NOTE  Entity adapted from rational_b_spline_curve in ISO 10303-42.
HISTORY  New entity in IFC4.
Attribute definitions
#AttributeTypeCardinalityDescription G
9WeightsDataIfcRealL[2:?] The supplied values of the weights.X
Weights
:=IfcListToArray(WeightsData,0,SELF\IfcBSplineCurve.UpperIndexOnControlPoints)
IfcRealA[0:UpperIndexOnControlPoints]The array of weights associated with the control points. This is derived from the weights data. X
Formal Propositions
RuleDescription
SameNumOfWeightsAndPointsThere shall be the same number of weights as control points.
WeightsGreaterZeroAll the weights shall have values greater than 0.0.
Inherited definitions from supertypes
Entity inheritance IfcBSplineCurveWithKnots IfcBSplineCurve IfcBoundedCurve IfcCurve IfcGeometricRepresentationItem IfcRepresentationItem
Attribute inheritance
#AttributeTypeCardinalityDescriptionG
IfcRepresentationItem
LayerAssignmentIfcPresentationLayerAssignment
@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
StyledByItemIfcStyledItem
@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)
IfcDimensionCountThe space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve. X
IfcBoundedCurve
PositioningElementIfcLinearPositioningElement
@Axis
? X
IfcBSplineCurve
1DegreeIfcInteger The algebraic degree of the basis functions.X
2ControlPointsListIfcCartesianPointL[2:?] The list of control points for the curve.X
3CurveFormIfcBSplineCurveForm Used to identify particular types of curve; it is for information only.X
4ClosedCurveIfcLogical Indication of whether the curve is closed; it is for information only.X
5SelfIntersectIfcLogical Indication whether the curve self-intersects or not; it is for information only.X
UpperIndexOnControlPoints
:=(SIZEOF(ControlPointsList) - 1)
IfcIntegerThe 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)
IfcCartesianPointA[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
6KnotMultiplicitiesIfcIntegerL[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
7KnotsIfcParameterValueL[2:?] The list of distinct knots used to define the B-spline basis functions.X
8KnotSpecIfcKnotType The description of the knot type. This is for information only.X
UpperIndexOnKnots
:=SIZEOF(Knots)
IfcIntegerThe upper index on the knot arrays; the lower index is 1. X
IfcRationalBSplineCurveWithKnots
9WeightsDataIfcRealL[2:?] The supplied values of the weights.X
Weights
:=IfcListToArray(WeightsData,0,SELF\IfcBSplineCurve.UpperIndexOnControlPoints)
IfcRealA[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;

Link to EXPRESS-G diagram EXPRESS-G diagram

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