8.9.3.54 IfcRationalBSplineSurfaceWithKnots
8.9.3.54.1 Semantic definition
A rational B-spline surface with knots is a piecewise parametric rational surface described in terms of control points, and associated weight values.
The surface is to be interpreted as follows:
8.9.3.54.2 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
8.9.3.54.3 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. |
|
IfcSurface (1) | |||
* | Dim | IfcDimensionCount |
This attribute is formally derived.
The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item. |
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. |
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. |
Click to show 20 hidden inherited attributes Click to hide 20 inherited attributes | |||
IfcRationalBSplineSurfaceWithKnots (2) | |||
13 | WeightsData | LIST [2:?] OF LIST [2:?] OF IfcReal |
The weights associated with the control points in the rational case. |
* | Weights | ARRAY [0:UUpper] OF ARRAY [0:VUpper] OF IfcReal |
This attribute is formally derived.
Array (two-dimensional) of weight values constructed from the WeightsData. |
8.9.3.54.4 Formal propositions
Name | Description |
---|---|
CorrespondingWeightsDataLists |
The array dimensions for the weights shall be consistent with the control points data. |
|
|
WeightValuesGreaterZero |
The weight value associated with each control point shall be greater than zero. |
|
8.9.3.54.5 Formal representation
ENTITY IfcRationalBSplineSurfaceWithKnots
SUBTYPE OF (IfcBSplineSurfaceWithKnots);
WeightsData : LIST [2:?] OF LIST [2:?] OF IfcReal;
DERIVE
Weights : ARRAY [0:UUpper] OF ARRAY [0:VUpper] OF IfcReal := IfcMakeArrayOfArray(WeightsData,0,UUpper,0,VUpper);
WHERE
CorrespondingWeightsDataLists : (SIZEOF(WeightsData) = SIZEOF(SELF\IfcBSplineSurface.ControlPointsList))
AND
(SIZEOF(WeightsData[1]) = SIZEOF(SELF\IfcBSplineSurface.ControlPointsList[1]));
WeightValuesGreaterZero : IfcSurfaceWeightsPositive(SELF);
END_ENTITY;