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.
QwtSpline &	operator= (const QwtSpline &)
void	setSplineType (SplineType)
SplineType	splineType () const
bool	setPoints (const QPolygonF &points)
	Calculate the spline coefficients. More...
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. More...
bool	buildPeriodicSpline (const QPolygonF &)
	Determines the coefficients for a periodic spline. More...

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

(

const QwtSpline &

other

)

Copy constructor

Parameters

other

Spline 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

other

Spline 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

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.

Parameters

x	Coordinate

Returns

Interpolated coordinate