Drawing QwtPlotCurve without deleting old data

Hello,
I am trying to plot (realtime) some lines for some sensor data without removing the older lines on the QwtPlot object from the past.

Code:

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m_Gui.guiQwtPlot->setTitle(title);
m_Gui.guiQwtPlot->setCanvasBackground(* new QBrush(Qt::black));
m_Gui.guiQwtPlot->setAxisScale(QwtPlot::yLeft, -30.0, 30.0);
m_Gui.guiQwtPlot->insertLegend(new QwtLegend());
m_Gui.guiQwtPlot->legend()->setFont(fontNormal);
m_Gui.guiQwtPlot->setFont(fontNormal);
m_Gui.guiQwtPlot->setAxisFont(QwtPlot::yLeft, fontNormal);
m_Gui.guiQwtPlot->setAxisFont(QwtPlot::xBottom, fontNormal);
m_Gui.guiQwtPlot->setAxisScaleDraw(QwtPlot::xBottom, new TimeScaleDraw(QTime::currentTime()));
m_Gui.guiQwtPlot->setAxisLabelRotation(QwtPlot::xBottom, 0.0);
m_Gui.guiQwtPlot->setAxisLabelAlignment(QwtPlot::xBottom,Qt::AlignLeft|Qt::AlignBottom);
m_Gui.guiQwtPlot->setAxisTitle(QwtPlot::xBottom, axisTitleBottom);
m_Gui.guiQwtPlot->setAxisTitle(QwtPlot::yLeft, axisTitleLeft);
 
QwtPlotMagnifier *plotM= new QwtPlotMagnifier(m_Gui.guiQwtPlot->canvas());
plotM->setMouseButton(Qt::NoButton);
 
QwtPlotPanner *plotP= new QwtPlotPanner(m_Gui.guiQwtPlot->canvas());

---

In every 5 seconds I get new data from sensors and for each sensor I create a QwtPlotCurve then update my sensor-data with setSamples(points)

Code:

---

void pcaPlotting::updateDataSlot(QString sensorId, QPolygonF points)
{
  QMap<QString, QwtPlotCurve*>  m_PlotC;
  QStringList  m_SensorNameList
 
  for(unsigned int i= 0; i< m_SensorNameList.count(); ++i)
  {  
    m_PlotC[m_SensorNameList.at(i)]= new QwtPlotCurve();
    m_PlotC[m_SensorNameList.at(i)]->setRenderHint(QwtPlotItem::RenderAntialiased, true);
    m_PlotC[m_SensorNameList.at(i)]->setCurveAttribute(QwtPlotCurve::Fitted);
  }
  m_PlotC[sensorId]->setSamples(points);
 
  emit updatePlotSignal(m_PlotC);
}

---

Finally I update my plot over signal/slot

Code:

---

void mainGui::updatePlotSlot(QMap<QString, QwtPlotCurve*> plotC)
{
  for(QMap<QString, QwtPlotCurve*>::iterator it= plotC.begin(); it!= plotC.end(); ++it)
  {
    plotC[it.key()]->attach(m_Gui.guiQwtPlot);
    m_Gui.guiQwtPlot->replot();
  }
}

---

My problem is: it plots only the data, those I got in 5 sec and then the lines are replaced with the new data after 5 sec. What should I do, so that the lines will not be replaced and increased until I stop drawing?
May be second question: The drawn data is not centered to the QwtPlot-window, it overflows in +y-axis, if the data is higher then the set boundaries setAxisScale(QwtPlot::yLeft, -30.0, 30.0); How can I draw in the center of y-axis, so that the size of the QwtPlot does not matter.

Thank you

Quote:

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Originally Posted by nasil122002

What should I do, so that the lines will not be replaced and increased until I stop drawing?

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Have a look at QwtPlotDirectPainter.
The realtime example shows how to use it. The oscilloscope is probably much closer to your use case, but the source code requires some time to understand how it works.

Quote:

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Originally Posted by nasil122002

How can I draw in the center of y-axis, so that the size of the QwtPlot does not matter.

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Not sure if I understand this one.

Uwe

Quote:

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Originally Posted by Uwe

Not sure if I understand this one.
Uwe

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Sorry for bad explanation. I found the solution by changing the yLeft- Axis scale from setAxisScale(QwtPlot::yLeft, -30.0, 30.0); to setAxisScale(QwtPlot::yLeft, -200.0, 200.0); Now the lines are aligned correctly

Ok I have adapted my code above to the QwtPlotDirectPainter real-time example.

By the initialization of QwtPlot I added additionally canvas()->setAttribute() and setAutoReplot() functions:

Code:

---

void guiMain::createPlot(QStringList m_SensorNameList)
 
m_Gui.guiQwtPlot->setTitle(title);
m_Gui.guiQwtPlot->setCanvasBackground(* new QBrush(Qt::black));
m_Gui.guiQwtPlot->setAxisScale(QwtPlot::yLeft, -30.0, 30.0);
m_Gui.guiQwtPlot->insertLegend(new QwtLegend());
m_Gui.guiQwtPlot->legend()->setFont(fontNormal);
m_Gui.guiQwtPlot->setFont(fontNormal);
m_Gui.guiQwtPlot->setAxisFont(QwtPlot::yLeft, fontNormal);
m_Gui.guiQwtPlot->setAxisFont(QwtPlot::xBottom, fontNormal);
m_Gui.guiQwtPlot->setAxisScaleDraw(QwtPlot::xBottom, new TimeScaleDraw(QTime::currentTime()));
m_Gui.guiQwtPlot->setAxisLabelRotation(QwtPlot::xBottom, 0.0);
m_Gui.guiQwtPlot->setAxisLabelAlignment(QwtPlot::xBottom,Qt::AlignLeft|Qt::AlignBottom);
m_Gui.guiQwtPlot->setAxisTitle(QwtPlot::xBottom, axisTitleBottom);
m_Gui.guiQwtPlot->setAxisTitle(QwtPlot::yLeft, axisTitleLeft);
m_Gui.guiQwtPlot->canvas()->setAttribute(Qt::WA_PaintOutsidePaintEvent, true);
m_Gui.guiQwtPlot->setAutoReplot(false);
 
QwtPlotMagnifier *plotM= new QwtPlotMagnifier(m_Gui.guiQwtPlot->canvas());
plotM->setMouseButton(Qt::NoButton);
 
QwtPlotPanner *plotP= new QwtPlotPanner(m_Gui.guiQwtPlot->canvas());

---

The initialization of QwtPlotCurve: For my each sensor, I create QwtPlotCurve, QwtPlotDirectPainter and add curveData to the QwtPlotCurve

Code:

---

void plotting::createPlotCurve(QStringList m_SensorNameList)
{
  QMap<QString, QwtPlotCurve*>  m_PlotC;
  QMap<QString, QwtPlotDirectPainter*> m_DirectPainter;
 
  if(!m_SensorNameList.isEmpty())
  {
    for(unsigned int i= 0; i< m_SensorNameList.count(); ++i)
    {
      m_PlotC[m_SensorNameList.at(i)]= new QwtPlotCurve();
      m_PlotC[m_SensorNameList.at(i)]->setPen(QPen(QColor(m_ColorList[i]), 1, Qt::SolidLine));
      m_PlotC[m_SensorNameList.at(i)]->setRenderHint(QwtPlotItem::RenderAntialiased, true);
      m_PlotC[m_SensorNameList.at(i)]->setCurveAttribute(QwtPlotCurve::Fitted);
 
      m_DirectPainter[m_SensorNameList.at(i)]= new QwtPlotDirectPainter();
      m_PlotC[m_SensorNameList.at(i)]->setData(new curveData());
    }
  }
}

---

After each 5 seconds, I get new data from sensors and for each sensor I append the QPolygonF points:

Code:

---

void plotting::updateDataSlot(QString sensorId, QPolygonF points)
{
  curveData *data= static_cast<curveData *>(m_PlotC[sensorId]->data());
  data->clear();
 
  if(m_SensorNameList.contains(sensorId))
  {
    //m_PlotC[sensorId]->setSamples(points);
 
    //curveData *data= static_cast<curveData *>(m_PlotC[sensorId]->data());
    data->append(points);
    m_DirectPainter[sensorId]->drawSeries(m_PlotC[sensorId], data->size()-100, data->size()-1);
 
    emit updatePlotSignal(m_PlotC);
  }
}

---

update plot:

Code:

---

void guiMain::updatePlotSlot(QMap<QString, QwtPlotCurve*> plotC)
{
  m_Gui.guiQwtPlot->repaint();
 
  for(QMap<QString, QwtPlotCurve*>::iterator it= plotC.begin(); it!= plotC.end(); ++it)
  {
    plotC[it.key()]->attach(m_Gui.guiQwtPlot);
    m_Gui.guiQwtPlot->replot();
  }
}

---

In curveData class I use QPolygonF insteat of QPointF in append function:

Code:

---

class curveData: public QwtArraySeriesData<QPointF>
{
public:
...
  inline void append(const QPolygonF &point)
  {
    d_samples+= point;
  }
...
};

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But somehow ,there is no difference with the previous plot. The lines are not appended and deleted from the scene after 5 sec. each time. If I comment out the m_Gui.guiQwtPlot->repaint(); then the lines are not cleared from the current plot but overlapped.