stereo_image_proc missing disparity output [closed]

edit

I was trying to use stereo_image_proc to perform stereo vision and hopefully can get a disparity map and some point clouds. I got both /camera_info & /image_raw topics from both cameras published however just nothing from /disparity... I am pretty sure I got all the topic names correct and double checked the connections between node with rxgraph. In case the cameras are not sync well, I set param "approximate_sync" to be True, however still nothing happened... Anybody knows what to do? Thanks in advance!