Plot only part of QwtCurve in real time plot

[SamuelNLP]

I have a QVector in which I'm constantly appending data so I can plot on a QwtPlot. But with a high frequency I guess the vector becames too large and the program crashes.

My question is, how can I create a QwtCurve which is only beggining in some point of time, bacause the time that has already passed is not necessary in the vector as it was already plotted.

here's my code:

QVector<double> xv;
QVector<double> cv1;
QVector<double> cv2;

QVector<double> xv;
QVector<double> cv1;
QVector<double> cv2;

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as global variables,

void gui::process_new_info(QByteArray array)
{
    int v = 0;
 
    double f = ui->frequency->value();
 
    xv.append(sizeof_array/f);
 
    char *buf = array.data();
 
    if (ui->ecgPlux->isChecked() == true || ui->channel_1->currentIndex() != 0)
    {
        cv1.append(buf[1]);
 
        QwtPlotCurve *curve1 = new QwtPlotCurve;
        curve1->attach(plot_all[0]);
        curve1->setData(xv,cv1);
        curve1->setPen(QPen(Qt::blue,1));
        plot_all[0]->replot();
 
        QwtPlotCurve *curve2 = new QwtPlotCurve;
        curve2->attach(plot[0]);
        curve2->setData(xv,cv1);
        curve2->setPen(QPen(Qt::blue,1));
        plot[0]->replot();
    }
 
    if (ui->xyzPlux->isChecked() == true || ui->channel_2->currentIndex() != 0)
    {
        cv2.append(buf[2]);
 
        QwtPlotCurve *curve3 = new QwtPlotCurve;
        curve3->attach(plot_all[1]);
        curve3->setData(xv,cv2);
        curve3->setPen(QPen(Qt::blue,1));
        plot_all[0]->replot();
 
        QwtPlotCurve *curve4 = new QwtPlotCurve;
        curve4->attach(plot[1]);
        curve4->setData(xv,cv1);
        curve4->setPen(QPen(Qt::blue,1));
        plot[1]->replot();
    }
 
    //printf ("%d ->", buf[0]);
    fprintf (data, "%d,", buf[0]);
 
    for (int i = 1; i < 9; i++)
    {
        v = buf[i];
        //printf ("%d,", v);
        fprintf (data, "%d,", v);
    }
 
    //printf ("\n");
    fprintf (data, "\n");
 
    sizeof_array++;
}

void gui::process_new_info(QByteArray array)
{
    int v = 0;

    double f = ui->frequency->value();

    xv.append(sizeof_array/f);

    char *buf = array.data();

    if (ui->ecgPlux->isChecked() == true || ui->channel_1->currentIndex() != 0)
    {
        cv1.append(buf[1]);

        QwtPlotCurve *curve1 = new QwtPlotCurve;
        curve1->attach(plot_all[0]);
        curve1->setData(xv,cv1);
        curve1->setPen(QPen(Qt::blue,1));
        plot_all[0]->replot();

        QwtPlotCurve *curve2 = new QwtPlotCurve;
        curve2->attach(plot[0]);
        curve2->setData(xv,cv1);
        curve2->setPen(QPen(Qt::blue,1));
        plot[0]->replot();
    }

    if (ui->xyzPlux->isChecked() == true || ui->channel_2->currentIndex() != 0)
    {
        cv2.append(buf[2]);

        QwtPlotCurve *curve3 = new QwtPlotCurve;
        curve3->attach(plot_all[1]);
        curve3->setData(xv,cv2);
        curve3->setPen(QPen(Qt::blue,1));
        plot_all[0]->replot();

        QwtPlotCurve *curve4 = new QwtPlotCurve;
        curve4->attach(plot[1]);
        curve4->setData(xv,cv1);
        curve4->setPen(QPen(Qt::blue,1));
        plot[1]->replot();
    }

    //printf ("%d ->", buf[0]);
    fprintf (data, "%d,", buf[0]);

    for (int i = 1; i < 9; i++)
    {
        v = buf[i];
        //printf ("%d,", v);
        fprintf (data, "%d,", v);
    }

    //printf ("\n");
    fprintf (data, "\n");

    sizeof_array++;
}

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[SamuelNLP]

I got it to work. I'll publish it later in case someone else needs it.

[honestapple]

Hi, SamuelNLP
I met the same question with you. How did you solve it? Would you like to publish your code? Thank you very much.

[krsree]

Sir,

I'm new to QT and QWT. Can u please give me a sample code of realtime plotting. My requirement is "Read the data [eg: Roll and Pitch] from a .bin file and plot based on time. I have tried.. but it is not plotting based on time

Thanks
Sree