IFC 4.3.0.1 (IFC4X3) development

8.9.3.6 IfcBSplineCurveWithKnots

8.9.3.6.1 Semantic definition

The IfcBSplineCurveWithKnots is a spline curve parameterized by spline functions for which the knot values are explicitly given.

8.9.3.6.2 Entity inheritance

8.9.3.6.3 Attributes

# Attribute Type Description
IfcRepresentationItem (2)
LayerAssignment SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems

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.

StyledByItem SET [0:1] OF IfcStyledItem FOR Item

Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve.

IfcCurve (1)
* Dim IfcDimensionCount

This attribute is formally derived.

IfcCurveDim(SELF)

The space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve.

IfcBSplineCurve (7)
1 Degree IfcInteger

The algebraic degree of the basis functions.

2 ControlPointsList LIST [2:?] OF IfcCartesianPoint

The list of control points for the curve.

3 CurveForm IfcBSplineCurveForm

Used to identify particular types of curve; it is for information only.

4 ClosedCurve IfcLogical

Indication of whether the curve is closed; it is for information only.

5 SelfIntersect IfcLogical

Indication whether the curve self-intersects or not; it is for information only.

* UpperIndexOnControlPoints IfcInteger

This attribute is formally derived.

(SIZEOF(ControlPointsList) - 1)

The upper index on the array of control points; the lower index is 0. This value is derived from the control points list.

* ControlPoints ARRAY [0:UpperIndexOnControlPoints] OF IfcCartesianPoint

This attribute is formally derived.

IfcListToArray(ControlPointsList,0,UpperIndexOnControlPoints)

The array of control points used to define the geometry of the curve. This is derived from the list of control points.

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IfcBSplineCurveWithKnots (4)
6 KnotMultiplicities LIST [2:?] OF IfcInteger

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.

7 Knots LIST [2:?] OF IfcParameterValue

The list of distinct knots used to define the B-spline basis functions.

8 KnotSpec IfcKnotType

The description of the knot type. This is for information only.

* UpperIndexOnKnots IfcInteger

This attribute is formally derived.

SIZEOF(Knots)

The upper index on the knot arrays; the lower index is 1.

Table 8.9.3.6.A

8.9.3.6.4 Formal propositions

Name Description
ConsistentBSpline

The function IfcConstraintsParamBSpline returns TRUE if no inconsistencies in the parametrisation of the B-spline are found.

IfcConstraintsParamBSpline(Degree, UpperIndexOnKnots,
UpperIndexOnControlPoints, KnotMultiplicities, Knots)
CorrespondingKnotLists

The number of elements in the knot multiplicities list shall be equal to the number of elements in the knots list.

SIZEOF(KnotMultiplicities) = UpperIndexOnKnots
Table 8.9.3.6.B

8.9.3.6.5 Formal representation

ENTITY IfcBSplineCurveWithKnots
 SUPERTYPE OF (ONEOF
	(IfcRationalBSplineCurveWithKnots))
 SUBTYPE OF (IfcBSplineCurve);
	KnotMultiplicities : LIST [2:?] OF IfcInteger;
	Knots : LIST [2:?] OF IfcParameterValue;
	KnotSpec : IfcKnotType;
 DERIVE
	 UpperIndexOnKnots : IfcInteger := SIZEOF(Knots);
 WHERE
	ConsistentBSpline : IfcConstraintsParamBSpline(Degree, UpperIndexOnKnots,
UpperIndexOnControlPoints, KnotMultiplicities, Knots);
	CorrespondingKnotLists : SIZEOF(KnotMultiplicities) = UpperIndexOnKnots;
END_ENTITY;

8.9.3.6.6 References

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8.9.3.6.7 Changelog

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