IfcBSplineSurfaceWithKnots

Item	Change	Description
IFC2x3 to IFC4
IfcBSplineSurfaceWithKnots	ADDED
IFC4 Addendum 1
IfcBSplineSurfaceWithKnots
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.

Semantic definitions at the entity

Entity definition

The IfcBSplineSurfaceWithKnots is a general form of rational or polynomial parametric surface in which the knot values are explicitly given.

NOTE 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.

NOTE Entity adapted from b_spline_surface_with_knots defined in ISO10303-42.

HISTORY New entity in IFC4.

Attribute definitions

#	Attribute	Type	Cardinality	Description	C
8	UMultiplicities	IfcInteger	L[2:?]	The multiplicities of the knots in the u parameter direction.	X
9	VMultiplicities	IfcInteger	L[2:?]	The multiplicities of the knots in the v parameter direction.	X
10	UKnots	IfcParameterValue	L[2:?]	The list of the distinct knots in the u parameter direction.	X
11	VKnots	IfcParameterValue	L[2:?]	The list of the distinct knots in the v parameter direction.	X
12	KnotSpec	IfcKnotType	[1:1]	The description of the knot type.	X
	KnotVUpper :=SIZEOF(VKnots)	IfcInteger	[1:1]	The number of distinct knots in the v parameter direction.	X
	KnotUUpper :=SIZEOF(UKnots)	IfcInteger	[1:1]	The number of distinct knots in the u parameter direction.	X

Formal Propositions

Rule	Description
UDirectionConstraints	The function returns TRUE when the parameter constraints are verified for the u direction.
VDirectionConstraints	The function returns TRUE when the parameter constraints are verified for the v direction.
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.

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	C
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.	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.	X
IfcGeometricRepresentationItem
IfcSurface
	Dim :=3	IfcDimensionCount	[1:1]	The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item.	X
IfcBoundedSurface
IfcBSplineSurface
1	UDegree	IfcInteger	[1:1]	Algebraic degree of basis functions in u.	X
2	VDegree	IfcInteger	[1:1]	Algebraic degree of basis functions in v.	X
3	ControlPointsList	IfcCartesianPoint	L[2:?]L[2:?]	This is a list of lists of control points.	X
4	SurfaceForm	IfcBSplineSurfaceForm	[1:1]	Indicator of special surface types.	X
5	UClosed	IfcLogical	[1:1]	Indication of whether the surface is closed in the u direction; this is for information only.	X
6	VClosed	IfcLogical	[1:1]	Indication of whether the surface is closed in the v direction; this is for information only.	X
7	SelfIntersect	IfcLogical	[1:1]	Flag to indicate whether, or not, surface is self-intersecting; this is for information only.	X
	UUpper :=SIZEOF(ControlPointsList) - 1	IfcInteger	[1:1]	Upper index on control points in u direction.	X
	VUpper :=SIZEOF(ControlPointsList[1]) - 1	IfcInteger	[1:1]	Upper index on control points in v direction.	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
IfcBSplineSurfaceWithKnots
8	UMultiplicities	IfcInteger	L[2:?]	The multiplicities of the knots in the u parameter direction.	X
9	VMultiplicities	IfcInteger	L[2:?]	The multiplicities of the knots in the v parameter direction.	X
10	UKnots	IfcParameterValue	L[2:?]	The list of the distinct knots in the u parameter direction.	X
11	VKnots	IfcParameterValue	L[2:?]	The list of the distinct knots in the v parameter direction.	X
12	KnotSpec	IfcKnotType	[1:1]	The description of the knot type.	X
	KnotVUpper :=SIZEOF(VKnots)	IfcInteger	[1:1]	The number of distinct knots in the v parameter direction.	X
	KnotUUpper :=SIZEOF(UKnots)	IfcInteger	[1:1]	The number of distinct knots in the u parameter direction.	X

Formal representations

XSD Specification

 <xs:element name="IfcBSplineSurfaceWithKnots" type="ifc:IfcBSplineSurfaceWithKnots" substitutionGroup="ifc:IfcBSplineSurface" nillable="true"/>

 <xs:complexType name="IfcBSplineSurfaceWithKnots">

  <xs:complexContent>

   <xs:extension base="ifc:IfcBSplineSurface">

    <xs:attribute name="UMultiplicities" use="optional">

     <xs:simpleType>

      <xs:restriction>

       <xs:simpleType>

        <xs:list itemType="ifc:IfcInteger"/>

       </xs:simpleType>

       <xs:minLength value="2"/>

      </xs:restriction>

     </xs:simpleType>

    </xs:attribute>

    <xs:attribute name="VMultiplicities" use="optional">

     <xs:simpleType>

      <xs:restriction>

       <xs:simpleType>

        <xs:list itemType="ifc:IfcInteger"/>

       </xs:simpleType>

       <xs:minLength value="2"/>

      </xs:restriction>

     </xs:simpleType>

    </xs:attribute>

    <xs:attribute name="UKnots" use="optional">

     <xs:simpleType>

      <xs:restriction>

       <xs:simpleType>

        <xs:list itemType="ifc:IfcParameterValue"/>

       </xs:simpleType>

       <xs:minLength value="2"/>

      </xs:restriction>

     </xs:simpleType>

    </xs:attribute>

    <xs:attribute name="VKnots" use="optional">

     <xs:simpleType>

      <xs:restriction>

       <xs:simpleType>

        <xs:list itemType="ifc:IfcParameterValue"/>

       </xs:simpleType>

       <xs:minLength value="2"/>

      </xs:restriction>

     </xs:simpleType>

    </xs:attribute>

    <xs:attribute name="KnotSpec" type="ifc:IfcKnotType" use="optional"/>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcBSplineSurfaceWithKnots

 SUPERTYPE OF(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

  UDirectionConstraints : IfcConstraintsParamBSpline (
  SELF\IfcBSplineSurface.UDegree, KnotUUpper, 
  SELF\IfcBSplineSurface.UUpper, UMultiplicities, UKnots);
  VDirectionConstraints : IfcConstraintsParamBSpline (
  SELF\IfcBSplineSurface.VDegree, KnotVUpper, 
  SELF\IfcBSplineSurface.VUpper, VMultiplicities, VKnots);
  CorrespondingULists : SIZEOF(UMultiplicities) = KnotUUpper;
  CorrespondingVLists : SIZEOF(VMultiplicities) = KnotVUpper;
END_ENTITY;

 EXPRESS-G diagram

	Bézier-Spline-Fläche mit (gegebenen) Kontrollpunkten
	BSpline Surface With Knots