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

#include <qwt_weeding_curve_fitter.h>

Inheritance diagram for QwtWeedingCurveFitter:

Public Member Functions
	QwtWeedingCurveFitter (double tolerance=1.0)

virtual	~QwtWeedingCurveFitter ()
	Destructor.

void	setTolerance (double)

double	tolerance () const

void	setChunkSize (uint)

uint	chunkSize () const

virtual QPolygonF	fitCurve (const QPolygonF &) const override

virtual QPainterPath	fitCurvePath (const QPolygonF &) const override

Public Member Functions inherited from QwtCurveFitter
virtual	~QwtCurveFitter ()
	Destructor.

Mode	mode () const

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

overridevirtual

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

overridevirtual

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