picker = new QwtPlotPicker(QwtPlot::xBottom,QwtPlot::yLeft,
QwtPicker::RectRubberBand,QwtPicker::AlwaysOn, myPlot->canvas());
QwtPickerDragRectMachine* test = new QwtPickerDragRectMachine();
test->setState(QwtPickerMachine::RectSelection);
picker->setStateMachine(test);

//connect(picker, SIGNAL(selected(const QPolygon)),this,SLOT( click_on_graph(const QPolygon)));
connect(picker, SIGNAL(selected(QRectF)),this,SLOT( click_on_graph(QRectF)));
}
void Mainwindow::click_on_graph(QRectF area)
{
int start;
int width=area.width();
start = curve->closestPoint(picker->trackerPosition());
qDebug()<<"index="<<start;
for(int i=0;i<=(width-1);i++)
{
QPointF graphintensity=this->curve->sample(start+(i));
qDebug()<<"x="<<graphintensity;
}
}
points 274 - 290
start point 274 and end point 290 in between only need to read
but here start is 282 and end is 297

x= QPointF(282.644,4.28082e+09)
x= QPointF(283.644,4.27951e+09)
x= QPointF(284.644,4.27911e+09)
x= QPointF(285.644,4.27898e+09)
x= QPointF(286.644,4.27898e+09)
x= QPointF(287.644,4.27898e+09)
x= QPointF(288.644,4.27891e+09)
x= QPointF(289.644,4.27885e+09)
x= QPointF(290.644,4.27885e+09)
x= QPointF(291.644,4.27891e+09)
x= QPointF(292.644,4.27891e+09)
x= QPointF(293.644,4.27878e+09)
x= QPointF(294.644,4.27885e+09)
x= QPointF(295.644,4.27885e+09)
x= QPointF(296.644,4.27885e+09)
x= QPointF(297.644,4.27891e+09)