def start(self):
        """ Start the sensor """
        # 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