Class Ifc4::IfcBSplineCurve¶
Defined in File Ifc4.h
Nested Relationships¶
This class is a nested type of Struct Ifc4.
Inheritance Relationships¶
Base Type¶
public Ifc4::IfcBoundedCurve
(Class Ifc4::IfcBoundedCurve)
Derived Type¶
public Ifc4::IfcBSplineCurveWithKnots
(Class Ifc4::IfcBSplineCurveWithKnots)
Class Documentation¶

class
Ifc4
::
IfcBSplineCurve
: public Ifc4::IfcBoundedCurve¶ Definition from ISO/CD 1030342:1992: A Bspline curve is a piecewise parametric polynomial or rational curve described in terms of control points and basis functions. The Bspline curve has been selected as the most stable format to represent all types of polynomial or rational parametric curves. With appropriate attribute values it is capable of representing single span or spline curves of explicit polynomial, rational, Bezier or Bspline type.
Interpretation of the data is as follows:
All weights shall be positive and the curve is given by
k+1 = number of control points
Pi = control points
wi = weights
d = degree
The knot array is an array of (k+d+2) real numbers [ud … uk+1], such that for all indices j in [d,k], uj <= uj+1. This array is obtained from the knot data list by repeating each multiple knot according to the multiplicity. N di, the ith normalized Bspline basis function of degree d, is defined on the subset [uid, … , ui+1] of this array.
Let L denote the number of distinct values among the d+k+2 knots in the knot array; L will be referred to as the ‘upper index on knots’. Let mj denote the multiplicity (number of repetitions) of the jth distinct knot. Then
All knot multiplicities except the first and the last shall be in the range 1 … degree; the first and last may have a maximum value of degree +
In evaluating the basis functions, a knot u of e.g. multiplicity 3 is interpreted as a string u, u, u, in the knot array. The Bspline curve has 3 special subtypes (Note: only 1, Bezier curve, included in this IFC release) where the knots and knot multiplicities are derived to provide simple default capabilities. Logical flag is provided to indicate whether the curve self intersects or not.
Figure 277 (from ISO 1030342) illustrates a Bspline curve.
Figure 277 — Bspline curve
NOTE Corresponding ISO 10303 entity: b_spline_curve. Please refer to ISO/IS 1030342:1994, p. 45 for the final definition of the formal standard.
HISTORY New entity in Release IFC2x2.
Subclassed by Ifc4::IfcBSplineCurveWithKnots
Public Types

typedef IfcTemplatedEntityList<IfcBSplineCurve>
list
¶
Public Functions

int
Degree
() const¶ The algebraic degree of the basis functions.

void
setDegree
(int v)¶

IfcTemplatedEntityList<::Ifc4::IfcCartesianPoint>::ptr
ControlPointsList
() const¶ The list of control points for the curve.

void
setControlPointsList
(IfcTemplatedEntityList<::Ifc4::IfcCartesianPoint>::ptr v)¶

::Ifc4::IfcBSplineCurveForm::Value
CurveForm
() const¶ Used to identify particular types of curve; it is for information only.

void
setCurveForm
(::Ifc4::IfcBSplineCurveForm::Value v)¶

bool
ClosedCurve
() const¶ Indication of whether the curve is closed; it is for information only.

void
setClosedCurve
(bool v)¶

bool
SelfIntersect
() const¶ Indication whether the curve selfintersects or not; it is for information only.

void
setSelfIntersect
(bool v)¶

IfcBSplineCurve
(IfcEntityInstanceData *e)¶

IfcBSplineCurve
(int v1_Degree, IfcTemplatedEntityList<::Ifc4::IfcCartesianPoint>::ptr v2_ControlPointsList, ::Ifc4::IfcBSplineCurveForm::Value v3_CurveForm, bool v4_ClosedCurve, bool v5_SelfIntersect)¶