Selecting QwtPlotCurve from QwtPlot

[Christoss]

Thank you for your answers, I used a mathematical equation that finds if the mouse point is on the line between the curves

[lwz]

I have looked into the curvetracker example and practiced . However , it can only locate the point on a straight line between two points without deviation . Deviation comes while the curve is set myplot->setCurveAttribute(QwtPlotCurve::Fitted) .

Any idea to fix this problem?
Thanks in advance !!

[Uwe]

Well, the fitter creates temporary points in paint device coordinates, that are not known to the picker. What you could do is to apply the spline interpolation to your points in plot coordinates ( using QwtSplineCurveFitter::fitCurve() manually ) passing the interpolated points instead. The curvetracker code works out of the box - but of course this is a different type of interpolation.

If you don't want to do this you could overload QwtSplineFitter::fitCurve() and store the interpolated points:

class YourSplineFitter: public QwtSplineFitter
{
public:
    virtual QPolygonF fitCurve( const QPolygonF &points ) const
    {
        mInterpolatedPoints = QwtSplineFitter::fitCurve( points );
        return mInterpolatedPoints; 
    }
 
    ...
private:
    QPolygonF mInterpolatedPoints;
};

class YourSplineFitter: public QwtSplineFitter
{
public:
    virtual QPolygonF fitCurve( const QPolygonF &points ) const
    {
        mInterpolatedPoints = QwtSplineFitter::fitCurve( points );
        return mInterpolatedPoints; 
    }

    ...
private:
    QPolygonF mInterpolatedPoints;
};

To copy to clipboard, switch view to plain text mode 

Then the CurveTracker can be implemented using mInterpolatePoints.

HTH,
Uwe

[lwz]

Thanks ,it works much better