sc = new QGraphicsScene(this);
  ui->graphicsView->setScene(sc);
  ui->graphicsView->setSceneRect(0,0,300,300);

  QGraphicsLineItem *li = new QGraphicsLineItem(1,1,100,100);
  li->setPen(QPen(Qt::black));
  QGraphicsLineItem *li2 = new QGraphicsLineItem(100,10,20,200);
  li2->setPen(QPen(Qt::black));
  QGraphicsItemGroup *ig = new QGraphicsItemGroup;
  ig->addToGroup(li);
  ig->addToGroup(li2);

  sc->addItem(ig);

  ig->moveBy(100,100);
  ig->rotate(10);

  QPointF p1,p2;

  p1 = ig->mapToScene(ig->mapFromItem(ig,QPointF(1,100)));
  p2 = ig->mapToScene(ig->mapFromItem(ig,QPointF(200,100)));

  QGraphicsLineItem *li3 = new QGraphicsLineItem(p1.x(),p1.y(),p2.x(),p2.y());

  li3->setPen(QPen(Qt::black));
  ig->addToGroup(li3);

p1 = ig->mapToScene(ig->mapFromItem(ig,QPointF(1,100))); 
p2 = ig->mapToScene(ig->mapFromItem(ig,QPointF(200,100)));

 p1 = ig->mapToScene(QPointF(1,100));
 p2 = ig->mapToScene(QPointF(200,100));