Question

I want to create something like the image below:

I’ve looked in the qwtplot documentation, but I think it is not possible to be done.

Anyone ever tried it?

Answer 1

Have a look at this question’s answer: Not Drawing QWT Plot Axis
You should create your own QwtScaleDraw subclass and redefine virtual QwtText label(double) const as described in the link to something like this:

    virtual QwtText label(double val) const
    {
         return QwtText(QString::number(val) + "s");
    }

For more information on format and precision of the value have a look here.

You can add a custom label using QwtPlotMarker.
This may look like this:

    QwtPlotMarker marker = new QwtPlotMarker();
    marker->attach(your_plot_instance);
    marker->setValue(0.0, 0.0); // location of the label in plot coordinates
    marker->setLabel("title");

If you want to set more properties for the plot marker, please have a look at the QwtPlotMarker doc