Class Ifc4x2::IfcBSplineSurface

Nested Relationships

This class is a nested type of Struct Ifc4x2.

Inheritance Relationships

Base Type

Derived Type

Class Documentation

class Ifc4x2::IfcBSplineSurface : public Ifc4x2::IfcBoundedSurface

Definition from 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.

The symbology used here is:

K1 = upper_index_on_u_control_points

K2 = upper_index_on_v_control_points

Pij = control_points

wij = weights

d1 = u_degree

d2 = v_degree

The control points are ordered as P00, P01, P02, ……, PK1(K2-1), PK1K2 The weights, in the case of the rational subtype, are ordered similarly.

For each parameter, s = u or v, if k is the upper index on the control points and d is the degree for s, the knot array is an array of (k

  • d + 2) real numbers [s-d, …., sk+1], such that for all indices j in [-d, k]; sj ≤ sj+1. This array is obtained from the appropriate u_knots or v_knots list by repeating each multiple knot according to the multiplicity.

Nid, the ith normalised B-spline basis function of degree d, is defined on the subset [si-d, …., si+1] of this array.

Let L denote the number of distinct values amongst the knots in the knot list; L will be referred to as the ‘upper index on knots’. Let mj denote the multiplicity (i.e., number of repetitions) of the jth distinct knot value. Then:

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.

The surface form is used to identify specific quadric surface types (which shall have degree two), ruled surfaces and surfaces of revolution. As with the b-spline curve, the surface form is informational only and the spline data takes precedence.

The surface is to be interpreted as follows: In the polynomial case the surface is given by the equation:

In the rational case the surface equation is:

NOTE Corresponding ISO 10303 entity: b_spline_surface. Please refer to ISO/IS 10303-42:1994, p. 78 for the final definition of the formal standard.

HISTORY New entity in IFC2x4.

Subclassed by Ifc4x2::IfcBSplineSurfaceWithKnots

Public Types

typedef IfcTemplatedEntityList<IfcBSplineSurface> list

Public Functions

int UDegree() const

Algebraic degree of basis functions in u.

void setUDegree(int v)
int VDegree() const

Algebraic degree of basis functions in v.

void setVDegree(int v)
IfcTemplatedEntityListList<::Ifc4x2::IfcCartesianPoint>::ptr ControlPointsList() const

This is a list of lists of control points.

void setControlPointsList(IfcTemplatedEntityListList<::Ifc4x2::IfcCartesianPoint>::ptr v)
::Ifc4x2::IfcBSplineSurfaceForm::Value SurfaceForm() const

Indicator of special surface types.

void setSurfaceForm(::Ifc4x2::IfcBSplineSurfaceForm::Value v)
bool UClosed() const

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

void setUClosed(bool v)
bool VClosed() const

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

void setVClosed(bool v)
bool SelfIntersect() const

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

void setSelfIntersect(bool v)
const IfcParse::entity &declaration() const
IfcBSplineSurface(IfcEntityInstanceData *e)
IfcBSplineSurface(int v1_UDegree, int v2_VDegree, IfcTemplatedEntityListList<::Ifc4x2::IfcCartesianPoint>::ptr v3_ControlPointsList, ::Ifc4x2::IfcBSplineSurfaceForm::Value v4_SurfaceForm, bool v5_UClosed, bool v6_VClosed, bool v7_SelfIntersect)

Public Static Functions

const IfcParse::entity &Class()