 libsurf
Programmer's Documentation

IgesSplineCurve Class Reference

Detailed Description

IGES 126 : Rational spline curve.

This class represents general rational spline curves (NURBS curves) in IGES files. Note that some CAD systems misuse this object to write plain lines (which should really be entity type 110) without setting the corresponding form attribute in the directory entry.

Spec : IGES 5.3 page 152

The rational B-spline curve may represent analytic curves of general interest. This information is important to both the sending and receiving systems. The Directory Entry Form Number Parameter is provided to communicate this information. For a brief description and a precise definition of rational B-spline curves, see Appendix B.

If the rational B-spline curve represents a preferred curve type, the form number corresponds to the ECO630 most preferred type. The preference order is from 1 through 5, followed by 0 For example, if the curve is a circle or circular arc, the form number shall be set to 2. If the curve is an ellipse with unequal major and minor axis lengths, the form number shall be set to 3. If the curve is not one of the preferred types, the form number shall be set to 0.

If the curve lies entirely within a unique plane, the planar flag (PROP1) shall be set to 1; otherwise it shall be set to 0 If it is set to 1, the plane normal (Parameters 14+A+4*K through 16+A+4*K) shall contain a unit vector normal to the plane containing the curve. These fields shall exist but are ignored if the curve is non-planar.

If the beginning and ending points on the curve, as defined by evaluating the curve at the starting and ending parameter values (i.e., V(0) and V(l)), are coincident, the curve is closed and PROP2 shall be set to 1. If they are not coincident, PROP2 shall be set to 0.

If the curve is rational (does not have all weights equal), PROP3 shall be set to 0 If all weights are ECO630 equal to each other, the curve is polynomial and PROP3 shall be set to 1. The curve is polynomial since in this case all weights cancel and the denominator reduces to one. (See Appendix B.) The weights shall be positive real numbers.

If the curve is periodic with respect to its parametric variable, PROP4 shall be set to 1; otherwise, PROP4 shall be set to 0 The periodic flag is to be interpreted as purely informational; the curves which are flagged to be periodic are to be evaluated exactly the same as in the non-periodic case.

Note that the control points are in the definition space of the curve.

IgesEntity, IgesFile

#include <iges126.h>

Inheritance diagram for IgesSplineCurve:
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Collaboration diagram for IgesSplineCurve:
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Public Member Functions

IgesSplineCurve ()
create undefined

void setup (int ncp, int degree, const double kts[], const double cp[])
pass data for polynomial spline curve

void setup (int ncp, int degree, const double kts[], const double wgt[], const double cp[])
pass data for rational spline curve

void flagClosed (bool f)
change closed flag

const Vector & knotVector () const
access knot vector

const PointList< 3 > & ctrlPoints () const
access control points

bool isPolynomial () const
is curve polynomial?

int degree () const
degree

void definition (IgesFile &file)
assemble definition

uint parse (const std::string &pds, const Indices &vpos)
parse entity data Public Member Functions inherited from IgesEntity
IgesEntity (int ety)
create entity type etype

virtual ~IgesEntity ()
destroy

int etype () const
entity type

int classOf () const
entity class identifier

void form (int f)
access the form field of the directory entry

void blank (int b)
access status field: blank (0/1)

void subswitch (int b)
access status field: subordinate switch (0-3)

void useflag (int b)
access status field: use flag (0-6)

void hierarchy (int b)
access status field: hierachy flag (0-2)

void trafoMatrix (int tfi)
access transformation matrix field

int trafoMatrix ()
access transformation matrix field

void label (const char *s)
set entity label (use only 8 characters)

std::string label () const
return label, if present

void subscript (int s)
set entity subscript

add reference to property/attribute table DE

uint pindex () const
parameter data index

uint nNoteRef () const
number of notes

uint nPropRef () const
number of property references

int noteRef (uint k) const
access note reference k

int propRef (uint k) const
access property reference k

int append (IgesFile &igfile)
append entity to file

bool retrieve (const IgesFile &igfile)
retrieve entity from file

Public Attributes

Vector knots
pointers to knots, weights and control points

Vector weights

PointList< 3, double > cpoints
control points

int k
number of control points minus one, degree

int m

int nknots

int planar
shape flags

int closed

int polynomial

int periodic

Vct3 nrm
unit normal if curve is planar

Real ustart
starting and ending parameter value

Real uend Public Types inherited from IgesEntity
enum  IgesEntityClass {
NoClass = 0, PointClass = 1, LineClass = 2, CurveClass = 4,
SurfaceClass = 8, StructureClass = 16, AnyClass = 31
} Static Public Member Functions inherited from IgesEntity
static IgesEntitycreate (const IgesDirEntry &e)
generate a new entity from code, return zero if not implemented

template<class EType >
static bool as (const IgesEntityPtr &ep, EType &t)
convenience function

static int classOf (int etype)
identity class of entity number Static Protected Member Functions inherited from IgesEntity
static int asInt (const char *s, int k)
convenience conversion function

static double asDouble (const char *s, int k)
convenience conversion function Protected Attributes inherited from IgesEntity
IgesDirEntry entry
directory entry

int plcpre
line counts in parameter section

int plcpost

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