8.9.3.8 IfcBSplineSurfaceWithKnots
8.9.3.8.1 Semantic definition
The IfcBSplineSurfaceWithKnots is a general form of rational or polynomial parametric surface in which the knot values are explicitly given.
Definition according to ISO/CD 10303-42:1992 This is a B-spline surface in which the knot values are explicitly given. This subtype shall be used to represent non-uniform B-spline surfaces, and may also be used for other knot types. 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. Entity adapted from b_spline_surface_with_knots defined in ISO10303-42. New entity in IFC4.8.9.3.8.2 Entity inheritance
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- IfcSurface
- IfcAnnotationFillArea
- IfcBooleanResult
- IfcBoundingBox
- IfcCartesianPointList
- IfcCartesianTransformationOperator
- IfcCsgPrimitive3D
- IfcCurve
- IfcDirection
- IfcFaceBasedSurfaceModel
- IfcFillAreaStyleHatching
- IfcFillAreaStyleTiles
- IfcGeometricSet
- IfcHalfSpaceSolid
- IfcLightSource
- IfcPlacement
- IfcPlanarExtent
- IfcPoint
- IfcSectionedSpine
- IfcSegment
- IfcShellBasedSurfaceModel
- IfcSolidModel
- IfcTessellatedItem
- IfcTextLiteral
- IfcVector
8.9.3.8.3 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. The inverse attribute LayerAssignments has been added. The inverse attribute LayerAssignment has been restricted to max 1. Upward compatibility for file based exchange is guaranteed. |
|
| 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. The inverse attribute StyledByItem has been added. |
|
| IfcSurface (1) | |||
| * | Dim | IfcDimensionCount |
This attribute is formally derived. The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item. Derived attribute promoted from subtypes. |
| IfcBSplineSurface (10) | |||
| 1 | UDegree | IfcInteger |
Algebraic degree of basis functions in u. |
| 2 | VDegree | IfcInteger |
Algebraic degree of basis functions in v. |
| 3 | ControlPointsList | LIST [2:?] OF LIST [2:?] OF IfcCartesianPoint |
This is a list of lists of control points. |
| 4 | SurfaceForm | IfcBSplineSurfaceForm |
Indicator of special surface types. |
| 5 | UClosed | IfcLogical |
Indication of whether the surface is closed in the u direction; this is for information only. |
| 6 | VClosed | IfcLogical |
Indication of whether the surface is closed in the v direction; this is for information only. |
| 7 | SelfIntersect | IfcLogical |
Flag to indicate whether, or not, surface is self-intersecting; this is for information only. |
| * | UUpper | IfcInteger |
This attribute is formally derived. Upper index on control points in u direction. |
| * | VUpper | IfcInteger |
This attribute is formally derived. Upper index on control points in v direction. |
| * | ControlPoints | ARRAY [0:UUpper] OF ARRAY [0:VUpper] OF IfcCartesianPoint |
This attribute is formally derived. Array (two-dimensional) of control points defining surface geometry. This array is constructed from the control points list. |
| Click to show 13 hidden inherited attributes Click to hide 13 inherited attributes | |||
| IfcBSplineSurfaceWithKnots (7) | |||
| 8 | UMultiplicities | LIST [2:?] OF IfcInteger |
The multiplicities of the knots in the u parameter direction. |
| 9 | VMultiplicities | LIST [2:?] OF IfcInteger |
The multiplicities of the knots in the v parameter direction. |
| 10 | UKnots | LIST [2:?] OF IfcParameterValue |
The list of the distinct knots in the u parameter direction. |
| 11 | VKnots | LIST [2:?] OF IfcParameterValue |
The list of the distinct knots in the v parameter direction. |
| 12 | KnotSpec | IfcKnotType |
The description of the knot type. |
| * | KnotVUpper | IfcInteger |
This attribute is formally derived. The number of distinct knots in the v parameter direction. |
| * | KnotUUpper | IfcInteger |
This attribute is formally derived. The number of distinct knots in the u parameter direction. |
8.9.3.8.4 Formal propositions
| Name | Description |
|---|---|
| CorrespondingULists |
The number of UMultiplicities shall be the same as the number of UKnots. |
|
|
| CorrespondingVLists |
The number of VMultiplicities shall be the same as the number of VKnots. |
|
|
| UDirectionConstraints |
The function returns TRUE when the parameter constraints are verified for the u direction. |
|
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| VDirectionConstraints |
The function returns TRUE when the parameter constraints are verified for the v direction. |
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8.9.3.8.5 Examples
8.9.3.8.6 Formal representation
ENTITY IfcBSplineSurfaceWithKnots
SUPERTYPE OF (ONEOF
(IfcRationalBSplineSurfaceWithKnots))
SUBTYPE OF (IfcBSplineSurface);
UMultiplicities : LIST [2:?] OF IfcInteger;
VMultiplicities : LIST [2:?] OF IfcInteger;
UKnots : LIST [2:?] OF IfcParameterValue;
VKnots : LIST [2:?] OF IfcParameterValue;
KnotSpec : IfcKnotType;
DERIVE
KnotVUpper : IfcInteger := SIZEOF(VKnots);
KnotUUpper : IfcInteger := SIZEOF(UKnots);
WHERE
CorrespondingULists : SIZEOF(UMultiplicities) = KnotUUpper;
CorrespondingVLists : SIZEOF(VMultiplicities) = KnotVUpper;
UDirectionConstraints : IfcConstraintsParamBSpline (
SELF\IfcBSplineSurface.UDegree, KnotUUpper,
SELF\IfcBSplineSurface.UUpper, UMultiplicities, UKnots);
VDirectionConstraints : IfcConstraintsParamBSpline (
SELF\IfcBSplineSurface.VDegree, KnotVUpper,
SELF\IfcBSplineSurface.VUpper, VMultiplicities, VKnots);
END_ENTITY;