howto get value at Tracker Point

[pospiech]

In my zoomer class I also set the tracker:

virtual QwtText trackerText( const QwtDoublePoint& p ) const 
    {
        QwtText t( QwtPlotPicker::trackerText( p ));
 
	QColor c(Qt::white);
        c.setAlpha(180);
        t.setBackgroundBrush( QBrush(c) );
 
        return t;
    }

virtual QwtText trackerText( const QwtDoublePoint& p ) const 
    {
        QwtText t( QwtPlotPicker::trackerText( p ));

	QColor c(Qt::white);
        c.setAlpha(180);
        t.setBackgroundBrush( QBrush(c) );

        return t;
    }

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This returns the axis coordinates.

I would also like to display the vlaue at the current point. However I do not know how to access this value at this point. The qwtPlot istself is known as the pointer 'plot' within the Zoomer class.

[StefanK]

Hello

I once implemented following method called by the trackerText() method. May be that helps?

bool PlotPicker::curveSelected(const QPoint pMousePos, PlotCurve* &pPlotCurve, double &pYValue) const
{
   double lDist = 10e10;
   int lIndex = -1;
 
   // get nearest curve point by iterating over plot items, filtering for curves and calculating minimum distance
   const QwtPlotItemList& lPlotItemList = plot()->itemList();
   for (QwtPlotItemIterator lPlotItemIterator = lPlotItemList.begin(); lPlotItemIterator != lPlotItemList.end(); ++lPlotItemIterator)
   {
      if ((*lPlotItemIterator)->rtti() == QwtPlotItem::Rtti_PlotCurve)
      {
         PlotCurve *lTmpCurve = (PlotCurve*)(*lPlotItemIterator);
 
         double lTmpDist;
         int lTmpIndex = lTmpCurve->closestPoint(pMousePos, &lTmpDist);
         if (lTmpDist < lDist && lTmpIndex > -1)
         {
            pPlotCurve = lTmpCurve;
            lDist = lTmpDist;
            lIndex = lTmpIndex;
         }
      }
   }
 
   // check if mouse position is in tolerance
   if (pPlotCurve && lDist < _pix_tolerance_)
   {
      pYValue = pPlotCurve->y(lIndex);
      return true;
   }
   pPlotCurve = 0;
   return false;
}

bool PlotPicker::curveSelected(const QPoint pMousePos, PlotCurve* &pPlotCurve, double &pYValue) const
{
   double lDist = 10e10;
   int lIndex = -1;

   // get nearest curve point by iterating over plot items, filtering for curves and calculating minimum distance
   const QwtPlotItemList& lPlotItemList = plot()->itemList();
   for (QwtPlotItemIterator lPlotItemIterator = lPlotItemList.begin(); lPlotItemIterator != lPlotItemList.end(); ++lPlotItemIterator)
   {
      if ((*lPlotItemIterator)->rtti() == QwtPlotItem::Rtti_PlotCurve)
      {
         PlotCurve *lTmpCurve = (PlotCurve*)(*lPlotItemIterator);

         double lTmpDist;
         int lTmpIndex = lTmpCurve->closestPoint(pMousePos, &lTmpDist);
         if (lTmpDist < lDist && lTmpIndex > -1)
         {
            pPlotCurve = lTmpCurve;
            lDist = lTmpDist;
            lIndex = lTmpIndex;
         }
      }
   }

   // check if mouse position is in tolerance
   if (pPlotCurve && lDist < _pix_tolerance_)
   {
      pYValue = pPlotCurve->y(lIndex);
      return true;
   }
   pPlotCurve = 0;
   return false;
}

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Within the trackerText() the call is..

//..... some preparations
   // check if tracker text shall be displayed
   if(mTrackerValueEnable)
   {
      double lSelectedYValue = 0.0;
      PlotCurve* lSelectedCurve = 0;
      if (curveSelected(pMousePos, lSelectedCurve, lSelectedYValue))
      {
         lLabel.append(QString("\n%1").arg(QString::number(lSelectedYValue)));
 //..... whatever needed
      }
   }
   QwtText lText(lLabel);
   QColor lBackground(Qt::lightGray);
   lBackground.setAlpha(_text_background_alpha_);
   lText.setBackgroundBrush(QBrush(lBackground));
   return lText;

//..... some preparations
   // check if tracker text shall be displayed
   if(mTrackerValueEnable)
   {
      double lSelectedYValue = 0.0;
      PlotCurve* lSelectedCurve = 0;
      if (curveSelected(pMousePos, lSelectedCurve, lSelectedYValue))
      {
         lLabel.append(QString("\n%1").arg(QString::number(lSelectedYValue)));
 //..... whatever needed
      }
   }
   QwtText lText(lLabel);
   QColor lBackground(Qt::lightGray);
   lBackground.setAlpha(_text_background_alpha_);
   lText.setBackgroundBrush(QBrush(lBackground));
   return lText;

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Regards
Stefan