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.

8.9.3.8.2 Entity inheritance

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.

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)

UDegree

IfcInteger

Algebraic degree of basis functions in u.

VDegree

IfcInteger

Algebraic degree of basis functions in v.

ControlPointsList

LIST [2:?] OF LIST [2:?] OF IfcCartesianPoint

This is a list of lists of control points.

SurfaceForm

IfcBSplineSurfaceForm

Indicator of special surface types.

UClosed

IfcLogical

Indication of whether the surface is closed in the u direction; this is for information only.

VClosed

IfcLogical

Indication of whether the surface is closed in the v direction; this is for information only.

SelfIntersect

IfcLogical

Flag to indicate whether, or not, surface is self-intersecting; this is for information only.

UUpper

IfcInteger

This attribute is formally derived.

SIZEOF(ControlPointsList) - 1

Upper index on control points in u direction.

VUpper

IfcInteger

This attribute is formally derived.

SIZEOF(ControlPointsList[1]) - 1

Upper index on control points in v direction.

ControlPoints

ARRAY [0:UUpper] OF ARRAY [0:VUpper] OF IfcCartesianPoint

This attribute is formally derived.

 IfcMakeArrayOfArray(ControlPointsList,
0,UUpper,0,VUpper)

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

IfcBSplineSurfaceWithKnots (7)

UMultiplicities

LIST [2:?] OF IfcInteger

The multiplicities of the knots in the u parameter direction.

VMultiplicities

LIST [2:?] OF IfcInteger

The multiplicities of the knots in the v parameter direction.

UKnots

LIST [2:?] OF IfcParameterValue

The list of the distinct knots in the u parameter direction.

VKnots

LIST [2:?] OF IfcParameterValue

The list of the distinct knots in the v parameter direction.

KnotSpec

IfcKnotType

The description of the knot type.

KnotVUpper

IfcInteger

This attribute is formally derived.

SIZEOF(VKnots)

The number of distinct knots in the v parameter direction.

KnotUUpper

IfcInteger

This attribute is formally derived.

SIZEOF(UKnots)

The number of distinct knots in the u parameter direction.

Table 8.9.3.8.C

8.9.3.8.4 Formal propositions

Name Description

CorrespondingULists

The number of UMultiplicities shall be the same as the number of UKnots.

SIZEOF(UMultiplicities) = KnotUUpper

CorrespondingVLists

The number of VMultiplicities shall be the same as the number of VKnots.

SIZEOF(VMultiplicities) = KnotVUpper

UDirectionConstraints

The function returns TRUE when the parameter constraints are verified for the u direction.

 IfcConstraintsParamBSpline (
  SELF\IfcBSplineSurface.UDegree, KnotUUpper, 
  SELF\IfcBSplineSurface.UUpper, UMultiplicities, UKnots)

VDirectionConstraints

The function returns TRUE when the parameter constraints are verified for the v direction.

 IfcConstraintsParamBSpline (
  SELF\IfcBSplineSurface.VDegree, KnotVUpper, 
  SELF\IfcBSplineSurface.VUpper, VMultiplicities, VKnots)

Table 8.9.3.8.D

8.9.3.8.5 Examples

Figure 8.9.3.8.A

Basin Advanced Brep
Figure 8.9.3.8.B

Cube Advanced Brep

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;

8.9.3.8 IfcBSplineSurfaceWithKnots

8.9.3.8.1 Semantic definition

8.9.3.8.2 Entity inheritance

8.9.3.8.3 Attributes

8.9.3.8.4 Formal propositions

8.9.3.8.5 Examples

8.9.3.8.6 Formal representation

8.9.3.8.7 References

8.9.3.8.8 Changelog

8.9.3.8.8.1 IFC4

	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;