in fact, i am using the aruco_ros and when i roslaunch the single.launch file, i can have the topic /single/pose /single/transform etc, but the problem is when the board aruco is out the sight of camera i get nothing for /single/transform, i know it's normal but what i want is when the aruco is out of sight i can get some msg for subscribing the topic of aruco, for example a flag false and i can use it in my code to express that the aruco is out of the camera