Qwt User's Guide: QwtSpline Class Reference

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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 QwtArray< double > & coefficientsA () const
const QwtArray< double > & coefficientsB () const
const QwtArray< double > & coefficientsC () const

Protected Member Functions

bool buildNaturalSpline (const QPolygonF &)
bool buildPeriodicSpline (const QPolygonF &)

Protected Attributes

PrivateData * d_data

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.

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 QwtArray< double > & QwtSpline::coefficientsA (  )  const
Returns:
A coefficients
const QwtArray< double > & QwtSpline::coefficientsB (  )  const
Returns:
B coefficients
const QwtArray< 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:
x 
y points
size number of points
periodic if true, calculate periodic spline
Returns:
true if successful
Warning:
The sequence of x (but not y) values has to be strictly monotone increasing, which means x[0] < x[1] < .... < x[n-1]. 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.

Generated on Wed Sep 2 18:37:27 2009 for Qwt User's Guide by  doxygen 1.6.1
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