qwtPlotPicker: simple problem to start understanding how it works

[fatecasino]

I have been reading several examples and threads about qwtPlotPicker, but most people have extreme problems for the standards of my understanding, so the solutions are more confusing than answering to my questions.

Problem

1. create a picker
2. when you click
3. you leave mark on the plot/canvas, a cross "+", an "x", whatever
4. get the clicked coordinates in a variable

So far, I have reached this point:

mypicker = new QwtPlotPicker(m_amp->canvas());
mypicker->setTrackerMode(QwtPicker::AlwaysOn);
mypicker->setRubberBand(QwtPicker::VLineRubberBand);//not sure for this!
mypicker->setSelectionFlags(QwtPicker::PointSelection | QwtPicker::ClickSelection);

mypicker = new QwtPlotPicker(m_amp->canvas());
mypicker->setTrackerMode(QwtPicker::AlwaysOn);
mypicker->setRubberBand(QwtPicker::VLineRubberBand);//not sure for this!
mypicker->setSelectionFlags(QwtPicker::PointSelection | QwtPicker::ClickSelection);

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any suggestions to move on?!