Get a smooth curve

[Uwe]

You can try to use a QwtCurveFitter:

a) QwtSplineCurveFitter
Spline interpolation avoids edges, when you don't have enough points.

b) QwtWeedingCurveFitter
This is an implementation of the Douglas-Peucker algorithm. In opposite to spline interpolation it decreases the number of points.

I guess QwtWeedingCurveFitter is what you are looking for. Unfortunately this is a new class you find in Qwt SVN trunk only. But AFAIR the class is compatible with Qwt 5.2. So you can copy it into your code - or add it to your 5.2 package.

QwtWeedingCurveFitter *fitter = new QwtWeedingCurveFitter();
fitter->setTolerance(...);
curve->setCurveFitter(fitter);
curve->setCurveAttribute(QwtPlotCurve::Fitted, true);

QwtWeedingCurveFitter *fitter = new QwtWeedingCurveFitter();
fitter->setTolerance(...);
curve->setCurveFitter(fitter);
curve->setCurveAttribute(QwtPlotCurve::Fitted, true);

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Uwe