Newbie : QwtCurveFitter and retrieve curve data

[sapym]

Gloups...
fitCurve(points) don't give the exact points that I can see on the plot ....

I can see on the graph some values always > 0 and in the PolygonF retrieved... I have some negative values...how can I retrieve the exact values of the plot ???

[Uwe]

Of course you have to assign the fitted points ( = points2 in your code snippet ) to your curve and disable QwtPlotCurve::Fitted.

Uwe

[sapym]

This is my code :

Plot::Plot(QWidget *parent):
    QwtPlot(parent)
{
    tab_x[0] = 0;    tab_x[1] = 200;    tab_x[2] = 400;    tab_x[3] = 600;    tab_x[4] = 1600;	tab_x[5] = 2000;
    tab_x[6] = 2400;	tab_x[7] = 2800;	tab_x[8] = 3200;	tab_x[9] = 3600;	tab_x[10] =     
 
    tab_y[0] = mygamma(tab_x[0],4096,1023,0.5);
    tab_y[1] = mygamma(tab_x[1],4096,1023,0.5);
    tab_y[2] = mygamma(tab_x[2],4096,1023,0.5);
    tab_y[3] = mygamma(tab_x[3],4096,1023,0.5);
    tab_y[4] = mygamma(tab_x[4],4096,1023,0.5);
    tab_y[5] = mygamma(tab_x[5],4096,1023,0.    
    tab_y[6] = mygamma(tab_x[6],4096,1023,0.5);
    tab_y[7] = mygamma(tab_x[7],4096,1023,0.5);
    tab_y[8] = mygamma(tab_x[8],4096,1023,0.5);
    tab_y[9] = mygamma(tab_x[9],4096,1023,0.5);
    tab_y[10] = mygamma(tab_x[10],4096,1023,0.5);
 
    int nb_points = sizeof(tab_x) / sizeof(tab_x[0]);
    QPolygonF points,points2;
    for ( int i = 0; i < nb_points ; i++ )
    {
        points += QPointF(tab_x[i], tab_y[i]);
    }
 
    m_Curve = new QwtPlotCurve();
    m_CurveFitter = new QwtSplineCurveFitter();
 
    m_Curve->setCurveAttribute(QwtPlotCurve::Fitted, true);	// Otherwise I have got Lines and not smooth curve the fitted curve is better for me
    m_Curve->setStyle(QwtPlotCurve::Lines);
 
    m_CurveFitter->setFitMode(m_CurveFitter->ParametricSpline);
    m_CurveFitter->setSplineSize(4096);                                           // from my orignal 10 points I want 4096 points			
 
    m_Curve->setCurveFitter(m_CurveFitter);			
    m_Curve->setData(tab_x, tab_y, sizeof(tab_x) / sizeof(tab_x[0]));
    m_Curve->attach(this);	
}
 
 
 
QPolygonF Plot::getPoints(int nCurve)
{	
	QPolygonF points,InterpolatedPoints;
m_Curve;
m_CurveFitter
 
    for ( int i = 0; i < m_Curve->dataSize(); i++ )
    {		
        points += QPointF(m_Curve->x(i), m_Curve->y(i));		
    }
 
    InterpolatedPoints = curveFitter->fitCurve(points);
 
    return InterpolatedPoints;
}
 
 
double mygamma(double in,int nbpoints_in,int nbpoints_out,double gma)
{
	double x = in / nbpoints_in;
 
	return (pow(x,gma) * nbpoints_out );
}

Plot::Plot(QWidget *parent):
    QwtPlot(parent)
{
    tab_x[0] = 0;    tab_x[1] = 200;    tab_x[2] = 400;    tab_x[3] = 600;    tab_x[4] = 1600;	tab_x[5] = 2000;
    tab_x[6] = 2400;	tab_x[7] = 2800;	tab_x[8] = 3200;	tab_x[9] = 3600;	tab_x[10] =     

    tab_y[0] = mygamma(tab_x[0],4096,1023,0.5);
    tab_y[1] = mygamma(tab_x[1],4096,1023,0.5);
    tab_y[2] = mygamma(tab_x[2],4096,1023,0.5);
    tab_y[3] = mygamma(tab_x[3],4096,1023,0.5);
    tab_y[4] = mygamma(tab_x[4],4096,1023,0.5);
    tab_y[5] = mygamma(tab_x[5],4096,1023,0.    
    tab_y[6] = mygamma(tab_x[6],4096,1023,0.5);
    tab_y[7] = mygamma(tab_x[7],4096,1023,0.5);
    tab_y[8] = mygamma(tab_x[8],4096,1023,0.5);
    tab_y[9] = mygamma(tab_x[9],4096,1023,0.5);
    tab_y[10] = mygamma(tab_x[10],4096,1023,0.5);
    
    int nb_points = sizeof(tab_x) / sizeof(tab_x[0]);
    QPolygonF points,points2;
    for ( int i = 0; i < nb_points ; i++ )
    {
        points += QPointF(tab_x[i], tab_y[i]);
    }
	       
    m_Curve = new QwtPlotCurve();
    m_CurveFitter = new QwtSplineCurveFitter();

    m_Curve->setCurveAttribute(QwtPlotCurve::Fitted, true);	// Otherwise I have got Lines and not smooth curve the fitted curve is better for me
    m_Curve->setStyle(QwtPlotCurve::Lines);

    m_CurveFitter->setFitMode(m_CurveFitter->ParametricSpline);
    m_CurveFitter->setSplineSize(4096);                                           // from my orignal 10 points I want 4096 points			
    		
    m_Curve->setCurveFitter(m_CurveFitter);			
    m_Curve->setData(tab_x, tab_y, sizeof(tab_x) / sizeof(tab_x[0]));
    m_Curve->attach(this);	
}



QPolygonF Plot::getPoints(int nCurve)
{	
	QPolygonF points,InterpolatedPoints;
m_Curve;
m_CurveFitter
			
    for ( int i = 0; i < m_Curve->dataSize(); i++ )
    {		
        points += QPointF(m_Curve->x(i), m_Curve->y(i));		
    }
	
    InterpolatedPoints = curveFitter->fitCurve(points);

    return InterpolatedPoints;
}


double mygamma(double in,int nbpoints_in,int nbpoints_out,double gma)
{
	double x = in / nbpoints_in;

	return (pow(x,gma) * nbpoints_out );
}

To copy to clipboard, switch view to plain text mode 

So I have to setCurveAttribute(QwtPlotCurve::Fitted, FALSE ); ?? I that case my curve is totally not smooth...
I don't understand how Qwt can trace a curve, and one cannot access the points of that curve...

I do understand in my code that the Interpolated points that I retrieve are not the one traced on my graph ..the Fitted parameter should change this ...but I need it.

[Uwe]

You have to interpolate your points first and then assign the interpolated points to to your curve. What's so hard about this ?

Uwe

[sapym]

Well...sorry to bother you ...how do you assign ? setData ?

points2 = m_CurveFitter->fitCurve(points);
m_Curve->setData(points2);

points2 = m_CurveFitter->fitCurve(points);
m_Curve->setData(points2);

To copy to clipboard, switch view to plain text mode 

if I do so : setData...my curve is made of 4096 points... and I cannot move the original points like I used to...

What I want to "capture" :

[Uwe]

if I do so : setData...my curve is made of 4096 points... and I cannot move the original points like I used to...

The interpolated points and your 4096 points are different - that's what spline interpolation is about. Of course you have to find a way to re-translate changes of the interpolated points into changes of your original ones.

Maybe it helps to insert 2 curves: one with your 4096 points with symbols only and a second one with the interpolated points showing the lines but no symbols ?


Uwe

[sapym]

I'm starting from 10 points : x_0 = 0 to x_10 = 4095 and y_0 = 0 to y_10 = 1023 y = f(x) with f = gamma function...

I used the "CanvasPicker" from the event_filter example to be abble to move these points ... the curve is modified at the same time... (setData (tab_x,tab_y,10) with tab_x and tab_y modified )

And from these 10 pôints ...I want the 4096 interpolated points (I don't see what you mean by "The interpolated points and your 4096 points are different")

[sapym]

I tried everything... from

curve->plot()->invTransform(curve->yAxis(), x);
or curve->plot()->transform(curve->yAxis(), x);
or curveFitter->spline().value(x);

Nothing...snif...

[Uwe]

Well, without understanding ( what is obvious from your code snippets ) what happens to your points you will fail. But what about the idea of using 2 QwtPlotCurves for your points: the first displaying the symbols only and a second one with a spline interpolated line ?

Uwe

[sapym]

Yes Uwe... I was a little stubborn and moreover kind of lost... please accept my appologies !
I know that my code is very far from perfect .. I do my best ... but as I said...a newbie...

I read this post form the beginning in order to have a fresh view on your advices and #4 is now clear to me...
Yes I tried yesterday with 2 curves ...

for (int ii = 0 ; ii < 2 ; ii ++)
	{
		m_UniqueCurve[ii] = new QwtPlotCurve();
		m_UniqueCurveFitter[ii] = new QwtSplineCurveFitter();
		m_UniqueCurveFitter[ii]->setFitMode(m_UniqueCurveFitter[ii]->ParametricSpline);
		m_UniqueCurveFitter[ii]->setSplineSize(4096);
		m_UniqueCurve[ii]->setCurveFitter(m_UniqueCurveFitter[ii]);		
	}
 
	m_UniqueCurve[0]->setCurveAttribute(QwtPlotCurve::Fitted, true);
	m_UniqueCurve[1]->setCurveAttribute(QwtPlotCurve::Fitted, false);
	m_UniqueCurve[0]->setStyle(QwtPlotCurve::Lines);
	m_UniqueCurve[1]->setStyle(QwtPlotCurve::Dots);
 
 
	m_UniqueCurve[0]->setPen(QColor(Qt::transparent));
	m_UniqueCurve[0]->setSymbol(QwtSymbol(QwtSymbol::Ellipse,Qt::gray, QColor(Qt::black), QSize(8,8)));
 
	m_UniqueCurve[1]->setPen(QColor(Qt::black));
 
        QPolygonF OriginalPoints,InterpolatedPoints;
	for ( int i = 0; i < TabX.count() ; i++ )
	{
		OriginalPoints+= QPointF(TabX[i], TabY[i]);
	}
 
	InterpolatedPoints= m_RedCurveFitter[1]->fitCurve(points);	
 
        m_UniqueCurve[0]->setData(TabX.data(), TabY.data(),TabX.count());		
	m_UniqueCurve[1]->setData(InterpolatedPoints);

for (int ii = 0 ; ii < 2 ; ii ++)
	{
		m_UniqueCurve[ii] = new QwtPlotCurve();
		m_UniqueCurveFitter[ii] = new QwtSplineCurveFitter();
		m_UniqueCurveFitter[ii]->setFitMode(m_UniqueCurveFitter[ii]->ParametricSpline);
		m_UniqueCurveFitter[ii]->setSplineSize(4096);
		m_UniqueCurve[ii]->setCurveFitter(m_UniqueCurveFitter[ii]);		
	}

	m_UniqueCurve[0]->setCurveAttribute(QwtPlotCurve::Fitted, true);
	m_UniqueCurve[1]->setCurveAttribute(QwtPlotCurve::Fitted, false);
	m_UniqueCurve[0]->setStyle(QwtPlotCurve::Lines);
	m_UniqueCurve[1]->setStyle(QwtPlotCurve::Dots);

	
	m_UniqueCurve[0]->setPen(QColor(Qt::transparent));
	m_UniqueCurve[0]->setSymbol(QwtSymbol(QwtSymbol::Ellipse,Qt::gray, QColor(Qt::black), QSize(8,8)));

	m_UniqueCurve[1]->setPen(QColor(Qt::black));

        QPolygonF OriginalPoints,InterpolatedPoints;
	for ( int i = 0; i < TabX.count() ; i++ )
	{
		OriginalPoints+= QPointF(TabX[i], TabY[i]);
	}

	InterpolatedPoints= m_RedCurveFitter[1]->fitCurve(points);	

        m_UniqueCurve[0]->setData(TabX.data(), TabY.data(),TabX.count());		
	m_UniqueCurve[1]->setData(InterpolatedPoints);

To copy to clipboard, switch view to plain text mode 

And then I had to patch some lines in tne canvaspicker to be abble to select the good curve and move them together...

So again I'm deeply sorry for hte bad quality of my code and my eyes while reading your posts

Thanks a lot for your help

Best regards

Paul