'Override to limit the bounds of the axis to the domain of the
transform.  In the case of Mercator, the bounds should be
limited to the threshold that was passed in.  Unlike the
autoscaling provided by the tick locators, this range limiting
will always be adhered to, whether the axis range is set
manually, determined automatically or changed through panning
and zooming.'

def limit_range_for_scale(self, vmin, vmax, minpos):

    return (max(vmin, (- self.thresh)), min(vmax, self.thresh))
