IfcRationalBSplineSurfaceWithKnots

BACnet MVD

#### IfcRationalBSplineSurfaceWithKnots

Natural language names

| Rationale Bézier-Spline - Oberfläche mit Kontrollpunkten
| Rational BSpline Surface With Knots
| Surfaces Bsplines rationnelles avec nœuds

Change log

Item | SPF | XML | Change | Description
--- | --- | --- | --- | ---
IFC2x3 to IFC4
IfcRationalBSplineSurfaceWithKnots |  |  | ADDED |
IFC4 Addendum 1
IfcRationalBSplineSurfaceWithKnots |  |  |  |
UDegree |  |  | MODIFIED | Type changed from INTEGER to IfcInteger.
VDegree |  |  | MODIFIED | Type changed from INTEGER to IfcInteger.
UClosed |  |  | MODIFIED | Type changed from LOGICAL to IfcLogical.
VClosed |  |  | MODIFIED | Type changed from LOGICAL to IfcLogical.
SelfIntersect |  |  | MODIFIED | Type changed from LOGICAL to IfcLogical.
UMultiplicities |  |  | MODIFIED | Type changed from INTEGER to IfcInteger.
VMultiplicities |  |  | MODIFIED | Type changed from INTEGER to IfcInteger.
WeightsData |  |  | MODIFIED | Type changed from REAL to IfcReal.

##### Semantic definitions at the entity

Entity 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:

> σ

> NOTE Entity adapted from rational_b_spline_surface in ISO 10303-42.

> HISTORY New entity in IFC4.

Attribute definitions

# | Attribute | Type | Cardinality | Description | B
--- | --- | --- | --- | --- | ---
13 | WeightsData | IfcReal | L[2:?] L[2:?] | The weights associated with the control points in the rational case. | X | X
| Weights :=IfcMakeArrayOfArray(WeightsData,0,UUpper,0,VUpper) | IfcReal | A[0:UUpper] A[0:VUpper] | Array (two-dimensional) of weight values constructed from the WeightsData. | X | X

Formal Propositions

Rule | 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.

##### Inherited definitions from supertypes

Entity inheritance
Attribute inheritance

# | Attribute | Type | Cardinality | Description | B
--- | --- | --- | --- | --- | ---
IfcRepresentationItem

LayerAssignment

IfcPresentationLayerAssignment
@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

StyledByItem

IfcStyledItem
@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

X

IfcGeometricRepresentationItem
IfcSurface

Dim
:=3

IfcDimensionCount

The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item.

> IFC4 CHANGE Derived attribute promoted from subtypes.

X

X

IfcBoundedSurface
IfcBSplineSurface
1 | UDegree | IfcInteger |  | Algebraic degree of basis functions in u. | X | X
2 | VDegree | IfcInteger |  | Algebraic degree of basis functions in v. | X | X
3 | ControlPointsList | IfcCartesianPoint | L[2:?] L[2:?] | This is a list of lists of control points. | X | X
4 | SurfaceForm | IfcBSplineSurfaceForm |  | Indicator of special surface types. | X | X
5 | UClosed | IfcLogical |  | Indication of whether the surface is closed in the u direction; this is for information only. | X | X
6 | VClosed | IfcLogical |  | Indication of whether the surface is closed in the v direction; this is for information only. | X | X
7 | SelfIntersect | IfcLogical |  | Flag to indicate whether, or not, surface is self-intersecting; this is for information only. | X | X
| UUpper :=SIZEOF(ControlPointsList) - 1 | IfcInteger |  | Upper index on control points in u direction. | X | X
| VUpper :=SIZEOF(ControlPointsList[1]) - 1 | IfcInteger |  | Upper index on control points in v direction. | X | X
| ControlPoints :=IfcMakeArrayOfArray(ControlPointsList, 0,UUpper,0,VUpper) | IfcCartesianPoint | A[0:UUpper] A[0:VUpper] | Array (two-dimensional) of control points defining surface geometry. This array is constructed from the control points list. | X | X
IfcBSplineSurfaceWithKnots
8 | UMultiplicities | IfcInteger | L[2:?] | The multiplicities of the knots in the u parameter direction. | X | X
9 | VMultiplicities | IfcInteger | L[2:?] | The multiplicities of the knots in the v parameter direction. | X | X
10 | UKnots | IfcParameterValue | L[2:?] | The list of the distinct knots in the u parameter direction. | X | X
11 | VKnots | IfcParameterValue | L[2:?] | The list of the distinct knots in the v parameter direction. | X | X
12 | KnotSpec | IfcKnotType |  | The description of the knot type. | X | X
| KnotVUpper :=SIZEOF(VKnots) | IfcInteger |  | The number of distinct knots in the v parameter direction. | X | X
| KnotUUpper :=SIZEOF(UKnots) | IfcInteger |  | The number of distinct knots in the u parameter direction. | X | X
IfcRationalBSplineSurfaceWithKnots
13 | WeightsData | IfcReal | L[2:?] L[2:?] | The weights associated with the control points in the rational case. | X | X
| Weights :=IfcMakeArrayOfArray(WeightsData,0,UUpper,0,VUpper) | IfcReal | A[0:UUpper] A[0:VUpper] | Array (two-dimensional) of weight values constructed from the WeightsData. | X | X

##### Formal representations

XML Specification
`<xs:element name="IfcRationalBSplineSurfaceWithKnots" type="ifc:IfcRationalBSplineSurfaceWithKnots" substitutionGroup="ifc:IfcBSplineSurfaceWithKnots" nillable="true"/>
<xs:complexType name="IfcRationalBSplineSurfaceWithKnots">
<xs:complexContent>
<xs:extension base="ifc:IfcBSplineSurfaceWithKnots">
<xs:sequence>
<xs:element name="WeightsData">
<xs:complexType>
<xs:sequence>
<xs:element ref="ifc:IfcReal-wrapper" minOccurs="4" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute ref="ifc:itemType" fixed="ifc:IfcReal-wrapper"/>
<xs:attribute ref="ifc:cType" fixed="list list"/>
<xs:attribute ref="ifc:arraySize" use="optional"/>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
`
EXPRESS Specification
`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;

EXPRESS-G diagram

`

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