QwtSpline Class Reference

A class for spline interpolation. More...

#include <qwt_spline.h>

List of all members.

Public Types
enum	SplineType {   Natural,   Periodic }
Public Member Functions
	QwtSpline ()
	QwtSpline (const QwtSpline &)
	~QwtSpline ()
QwtSpline &	operator= (const QwtSpline &)
void	setSplineType (SplineType)
SplineType	splineType () const
bool	setPoints (const QPolygonF &points)
QPolygonF	points () const
void	reset ()
bool	isValid () const
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 &)
bool	buildPeriodicSpline (const QPolygonF &)

---

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

enum QwtSpline::SplineType

Spline type.

Enumerator:

Natural	A natural spline.
Periodic	A periodic spline.

---

Constructor & Destructor Documentation

QwtSpline::QwtSpline

(

)

Constructor.

QwtSpline::QwtSpline

(

const QwtSpline &

other

)

Copy constructor

Parameters:

other

Spline used for initilization

QwtSpline::~QwtSpline

(

)

Destructor.

---

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

bool QwtSpline::isValid

(

)

const

True if valid.

QwtSpline & QwtSpline::operator=

(

const QwtSpline &

other

)

Assignment operator

Parameters:

other

Spline used for initilization

QPolygonF QwtSpline::points

(

)

const

Return points passed by setPoints

void QwtSpline::reset

(

)

Free allocated memory and set size to 0.

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:

points

Points

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:

splineType

Spline type

See also:

splineType()

QwtSpline::SplineType QwtSpline::splineType

(

)

const

Returns:

the spline type

See also:

setSplineType()

double QwtSpline::value

(

double

x

)

const

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