QwtWeedingCurveFitter Class Reference

A curve fitter implementing Douglas and Peucker algorithm. More...

#include <qwt_weeding_curve_fitter.h>

Inheritance diagram for QwtWeedingCurveFitter:

Classes
class	Line
class	PrivateData

Public Member Functions
uint	chunkSize () const
virtual QPolygonF	fitCurve (const QPolygonF &) const QWT_OVERRIDE
virtual QPainterPath	fitCurvePath (const QPolygonF &) const QWT_OVERRIDE
	QwtWeedingCurveFitter (double tolerance=1.0)
void	setChunkSize (uint)
void	setTolerance (double)
double	tolerance () const
virtual	~QwtWeedingCurveFitter ()
	Destructor. More...
Public Member Functions inherited from QwtCurveFitter
Mode	mode () const
virtual	~QwtCurveFitter ()
	Destructor. More...

Private Member Functions
virtual QPolygonF	simplify (const QPolygonF &) const

Private Attributes
PrivateData *	m_data

Additional Inherited Members
Public Types inherited from QwtCurveFitter
enum	Mode { Polygon, Path }
	Preferred mode of the fitting algorithm. More...
Protected Member Functions inherited from QwtCurveFitter
	QwtCurveFitter (Mode mode)

Detailed Description

A curve fitter implementing Douglas and Peucker algorithm.

The purpose of the Douglas and Peucker algorithm is that given a 'curve' composed of line segments to find a curve not too dissimilar but that has fewer points. The algorithm defines 'too dissimilar' based on the maximum distance (tolerance) between the original curve and the smoothed curve.

The runtime of the algorithm increases non linear ( worst case O( n*n ) ) and might be very slow for huge polygons. To avoid performance issues it might be useful to split the polygon ( setChunkSize() ) and to run the algorithm for these smaller parts. The disadvantage of having no interpolation at the borders is for most use cases irrelevant.

The smoothed curve consists of a subset of the points that defined the original curve.

In opposite to QwtSplineCurveFitter the Douglas and Peucker algorithm reduces the number of points. By adjusting the tolerance parameter according to the axis scales QwtSplineCurveFitter can be used to implement different level of details to speed up painting of curves of many points.

Definition at line 38 of file qwt_weeding_curve_fitter.h.

Constructor & Destructor Documentation

QwtWeedingCurveFitter()

QwtWeedingCurveFitter::QwtWeedingCurveFitter ( double  tolerance = 1.0 )

explicit

Constructor

Parameters

tolerance

Tolerance

See also

setTolerance(), tolerance()

Definition at line 50 of file qwt_weeding_curve_fitter.cpp.

~QwtWeedingCurveFitter()

QwtWeedingCurveFitter::~QwtWeedingCurveFitter ( )

virtual

Destructor.

Definition at line 58 of file qwt_weeding_curve_fitter.cpp.

Member Function Documentation

chunkSize()

uint QwtWeedingCurveFitter::chunkSize

(

)

const

Returns

Maximum for the number of points passed to a run of the algorithm - or 0, when unlimited

See also

setChunkSize()

Definition at line 114 of file qwt_weeding_curve_fitter.cpp.

fitCurve()

QPolygonF QwtWeedingCurveFitter::fitCurve ( const QPolygonF &  points ) const

virtual

Parameters

points

Series of data points

Returns

Curve points

See also

fitCurvePath()

Implements QwtCurveFitter.

Definition at line 124 of file qwt_weeding_curve_fitter.cpp.

fitCurvePath()

QPainterPath QwtWeedingCurveFitter::fitCurvePath ( const QPolygonF &  points ) const

virtual

Parameters

points

Series of data points

Returns

Curve path

See also

fitCurve()

Implements QwtCurveFitter.

Definition at line 151 of file qwt_weeding_curve_fitter.cpp.

setChunkSize()

void QwtWeedingCurveFitter::setChunkSize

(

uint

numPoints

)

Limit the number of points passed to a run of the algorithm

The runtime of the Douglas Peucker algorithm increases non linear with the number of points. For a chunk size > 0 the polygon is split into pieces passed to the algorithm one by one.

Parameters

numPoints

Maximum for the number of points passed to the algorithm

See also

chunkSize()

Definition at line 101 of file qwt_weeding_curve_fitter.cpp.

setTolerance()

void QwtWeedingCurveFitter::setTolerance

(

double

tolerance

)

Assign the tolerance

The tolerance is the maximum distance, that is acceptable between the original curve and the smoothed curve.

Increasing the tolerance will reduce the number of the resulting points.

Parameters

tolerance

Tolerance

See also

tolerance()

Definition at line 76 of file qwt_weeding_curve_fitter.cpp.

simplify()

QPolygonF QwtWeedingCurveFitter::simplify ( const QPolygonF &  points ) const

privatevirtual

Definition at line 158 of file qwt_weeding_curve_fitter.cpp.

tolerance()

double QwtWeedingCurveFitter::tolerance

(

)

const

Returns

Tolerance

See also

setTolerance()

Definition at line 85 of file qwt_weeding_curve_fitter.cpp.

Member Data Documentation

m_data

PrivateData* QwtWeedingCurveFitter::m_data

private

Definition at line 65 of file qwt_weeding_curve_fitter.h.

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The documentation for this class was generated from the following files:

• qwt_weeding_curve_fitter.h
• qwt_weeding_curve_fitter.cpp