Selecting QwtPlotCurve from QwtPlot

[Christoss]

You are also right, but still this finds only when the user clicks on a point. I'd like to select the line between the points as well

[jesse_mark]

well, this way its all depends :
- the Distance Between different Points on a curve(DBP),
- the Distance Between the different Curves(DBCs).

you may just need to use better tolerance distance to meet your needs. (if DBP is less than the DBCs ).

[Uwe]

Also have a look at the curvetracker example - maybe you find some interesting code snippet there too.

Uwe

[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;
};

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Then the CurveTracker can be implemented using mInterpolatePoints.

HTH,
Uwe

[lwz]

Thanks ,it works much better