Thanks for all your help !

I have now another problem...perhas should I start another thread ?

I have now my plot which I made using the event_filter example : I'm moving points of my curve and I am abble to save them... But I want to have the coordinates of my cursor on the plot...

So I tried to combine the bode example with QwtPlotZoomer or QwtPlotPicker... but my canvaspicker class (extracted from event_filter example) installs an eventFilter on the canvas ...so no click seems to be linked to the Picker...