|Qwt User's Guide
QwtWeedingCurveFitter - A curve fitter implementing Douglas and Peucker algorithm.
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
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.
Definition at line 50 of file qwt_weeding_curve_fitter.cpp.
Definition at line 114 of file qwt_weeding_curve_fitter.cpp.
Definition at line 124 of file qwt_weeding_curve_fitter.cpp.
QPainterPath QwtWeedingCurveFitter::fitCurvePath (const QPolygonF & points) const [override], [virtual]
Definition at line 151 of file qwt_weeding_curve_fitter.cpp.
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.
Definition at line 101 of file qwt_weeding_curve_fitter.cpp.
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.
Definition at line 76 of file qwt_weeding_curve_fitter.cpp.
Definition at line 85 of file qwt_weeding_curve_fitter.cpp.
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|Sun Jul 18 2021