QwtWeedingCurveFitter(3)

NAME
QwtWeedingCurveFitter - A curve fitter implementing Douglas and Peucker algorithm.

SYNOPSIS

#include <qwt_curve_fitter.h>

Inherits QwtCurveFitter.

  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

  Additional Inherited Members

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.

Constructor & Destructor Documentation

  QwtWeedingCurveFitter::QwtWeedingCurveFitter (double tolerance = 1.0)
Constructor

Parameters:
    tolerance Tolerance

See also:
    setTolerance(), tolerance()

Member Function Documentation

  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()

  QPolygonF QwtWeedingCurveFitter::fitCurve (const QPolygonF & points) const [virtual]

Parameters:
    points Series of data points

Returns:
    Curve points

Implements QwtCurveFitter.

  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()

  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()

  double QwtWeedingCurveFitter::tolerance () const

Returns:
    Tolerance

See also:
    setTolerance()

Author

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