Quote Originally Posted by rockinfresh View Post
... why is there another vector needed for the setSamples() of curve?
You have the option to copy your samples into a type of buffer that can be handled by QwtPlotCurve out of the box - or you can tell the curve how to read from your vector<byte> buffer:
simply derive from QwtSeriesData<QPointF>: http://qwt.sourceforge.net/class_qwt_series_data.html

Uwe