Arbitrary axis interval without affecting the plot

[Uwe]

My task is to create a clone for the Matlab imagesc() which has one form where one can specify the axis extents in the arguments.

See QwtPlot::setAxisScale() and check the spectrogram example how to eliminate the margins. If you want to limit the area, where to display your spectrogram see QwtRasterData::setInterval().

What the heck is your motivation to manipulate the canvas maps ?

Uwe