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.
Figure 8.9.3.6.A All knot multiplicities except the first and the last shall be in the range 1,...,d; the first and last may have a maximum value of d + 1. In evaluating the basis functions, a knot u of, e.g., multiplicity 3 is interpreted as a sequence u, u, u,; in the knot array.
8.9.3.6.2 Entity inheritance
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- IfcCurve
- IfcAnnotationFillArea
- IfcBooleanResult
- IfcBoundingBox
- IfcCartesianPointList
- IfcCartesianTransformationOperator
- IfcCsgPrimitive3D
- IfcDirection
- IfcFaceBasedSurfaceModel
- IfcFillAreaStyleHatching
- IfcFillAreaStyleTiles
- IfcGeometricSet
- IfcHalfSpaceSolid
- IfcLightSource
- IfcPlacement
- IfcPlanarExtent
- IfcPoint
- IfcSectionedSpine
- IfcSegment
- IfcShellBasedSurfaceModel
- IfcSolidModel
- IfcSurface
- IfcTessellatedItem
- IfcTextLiteral
- IfcVector
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. 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. 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. The array of control points used to define the geometry of the curve. This is derived from the list of control points. |
| Click to show 10 hidden inherited attributes Click to hide 10 inherited attributes | |||
| 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. The upper index on the knot arrays; the lower index is 1. |
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. |
|
|
| CorrespondingKnotLists |
The number of elements in the knot multiplicities list shall be equal to the number of elements in the knots list. |
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8.9.3.6.5 Examples
8.9.3.6.6 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;