Qwt User's Guide
QwtSpline Class Reference

A class for spline interpolation. More...

#include <qwt_spline.h>

Public Types

enum  SplineType { Natural, Periodic }
 Spline type. More...

Public Member Functions

 QwtSpline ()
 Constructor.
 QwtSpline (const QwtSpline &)
 ~QwtSpline ()
 Destructor.
QwtSplineoperator= (const QwtSpline &)
void setSplineType (SplineType)
SplineType splineType () const
bool setPoints (const QPolygonF &points)
 Calculate the spline coefficients.
QPolygonF points () const
void reset ()
 Free allocated memory and set size to 0.
bool isValid () const
 True if valid.
double value (double x) const
const QVector< double > & coefficientsA () const
const QVector< double > & coefficientsB () const
const QVector< double > & coefficientsC () const

Protected Member Functions

bool buildNaturalSpline (const QPolygonF &)
 Determines the coefficients for a natural spline.
bool buildPeriodicSpline (const QPolygonF &)
 Determines the coefficients for a periodic spline.

Detailed Description

A class for spline interpolation.

The QwtSpline class is used for cubical spline interpolation. Two types of splines, natural and periodic, are supported.

Usage:
  1. First call setPoints() to determine the spline coefficients for a tabulated function y(x).
  2. After the coefficients have been set up, the interpolated function value for an argument x can be determined by calling QwtSpline::value().
Example:
#include <qwt_spline.h>

QPolygonF interpolate(const QPolygonF& points, int numValues)
{
    QwtSpline spline;
    if ( !spline.setPoints(points) )
        return points;

    QPolygonF interpolatedPoints(numValues);

    const double delta =
        (points[numPoints - 1].x() - points[0].x()) / (points.size() - 1);
    for(i = 0; i < points.size(); i++)  / interpolate
    {
        const double x = points[0].x() + i * delta;
        interpolatedPoints[i].setX(x);
        interpolatedPoints[i].setY(spline.value(x));
    }
    return interpolatedPoints;
}

Member Enumeration Documentation

Spline type.

Enumerator:
Natural 

A natural spline.

Periodic 

A periodic spline.


Constructor & Destructor Documentation

QwtSpline::QwtSpline ( const QwtSpline other)

Copy constructor

Parameters:
otherSpline used for initialization

Member Function Documentation

bool QwtSpline::buildNaturalSpline ( const QPolygonF &  points) [protected]

Determines the coefficients for a natural spline.

Returns:
true if successful
bool QwtSpline::buildPeriodicSpline ( const QPolygonF &  points) [protected]

Determines the coefficients for a periodic spline.

Returns:
true if successful
const QVector< double > & QwtSpline::coefficientsA ( ) const
Returns:
A coefficients
const QVector< double > & QwtSpline::coefficientsB ( ) const
Returns:
B coefficients
const QVector< double > & QwtSpline::coefficientsC ( ) const
Returns:
C coefficients
QwtSpline & QwtSpline::operator= ( const QwtSpline other)

Assignment operator

Parameters:
otherSpline used for initialization
Returns:
*this
QPolygonF QwtSpline::points ( ) const
Returns:
Points, that have been by setPoints()
bool QwtSpline::setPoints ( const QPolygonF &  points)

Calculate the spline coefficients.

Depending on the value of periodic, this function will determine the coefficients for a natural or a periodic spline and store them internally.

Parameters:
pointsPoints
Returns:
true if successful
Warning:
The sequence of x (but not y) values has to be strictly monotone increasing, which means points[i].x() < points[i+1].x(). If this is not the case, the function will return false
void QwtSpline::setSplineType ( SplineType  splineType)

Select the algorithm used for calculating the spline

Parameters:
splineTypeSpline type
See also:
splineType()
Returns:
the spline type
See also:
setSplineType()
double QwtSpline::value ( double  x) const

Calculate the interpolated function value corresponding to a given argument x.

Parameters:
xCoordinate
Returns:
Interpolated coordinate

List of all members.

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