The IfcBSplineSurface is a general form of rational or polynomial parametric surface.
NOTE Definition according to ISO/CD 10303-42:1992
A b_spline_surface is a general form of rational or polynomial parametric surface which is represented by control points, basis functions, and possibly, weights. As with the corresponding curve entity it has some special subtypes where some of the data can be derived.
P00, P01, P02, ......, PK1(K2-1), PK1K2The weights, in the case of the rational subtype, are ordered similarly.
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.
In the rational case the surface equation is:
NOTE Entity adapted from b_spline_surface defined in ISO10303-42.
HISTORY New entity in IFC4.
|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.|
> 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.
|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.|
> IFC2x3 CHANGE The inverse attribute StyledByItem has been added.
|Dim||INVALID||The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item.|
> IFC4 CHANGE Derived attribute promoted from subtypes.
|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||INVALID||Upper index on control points in u direction.|
|VUpper||INVALID||Upper index on control points in v direction.|
|ControlPoints||INVALID||Array (two-dimensional) of control points defining surface geometry. This array is constructed from the control points list.|
ENTITY IfcBSplineSurface ABSTRACT SUPERTYPE OF (ONEOF (IfcBSplineSurfaceWithKnots)) SUBTYPE OF (IfcBoundedSurface); UDegree : IfcInteger; VDegree : IfcInteger; ControlPointsList : LIST [2:?] OF LIST [2:?] OF IfcCartesianPoint; SurfaceForm : IfcBSplineSurfaceForm; UClosed : IfcLogical; VClosed : IfcLogical; SelfIntersect : IfcLogical; DERIVE UUpper : IfcInteger := SIZEOF(ControlPointsList) - 1; VUpper : IfcInteger := SIZEOF(ControlPointsList) - 1; ControlPoints : ARRAY [0:UUpper] OF ARRAY [0:VUpper] OF IfcCartesianPoint := IfcMakeArrayOfArray(ControlPointsList, 0,UUpper,0,VUpper); END_ENTITY;