code: def start(self):
          
          # initialize subscribers
          self._pointcloud_sub = rospy.Subscriber('/%s/depth/points' %(self.frame), PointCloud2, self._pointcloud_callback)
          self._camera_info_sub = rospy.Subscriber('/%s/left/camera_info' %(self.frame), CameraInfo, self._camera_info_callback)
  
          while self._camera_intr is None:
              time.sleep(0.1)
          
          self._running = True
docs: Start the sensor