Based on uwsim, I want to set the orientation of multibeam to make it point downward [closed]

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I want to set the orientation of multibeam to make it point downward. In this way it can scan the terrain. Then I want to make another multibeam sensor forward so that it can find the obstacle. I put the visible tag in the scene file so that it would be much easier for me to set its orientation, but the beam is still invisible. Can anyone help me to make it visible or tell me the correct orientation of multibeam sensor?