Posted by matlabbe on URL: http://official-rtab-map-forum.206.s1.nabble.com/Mapping-with-two-robots-tp9736p9739.html
Are the two robots running an independent ROS master? or are they running with same ROS master? If they run with same ROS master, you have to launch both rtabmap nodes in different namespaces (same for all nodes running on each robot actually). You should also change the name of the TF frames (map_frame_id) accordingly (including robot's static TF too). Once the TF trees of the robots are in their respective namespace, you may launch two rviz, one with global frame set to root frame of robot 1, and the other one with root frame of robot 2.
If the robots are running their own ROS master, you may open two terminals on your remote computer and set the ROS_MASTER_URI accordingly in the terminals, then launch two rviz. I guess it is the easiest way to do it.