how to save explored unknown map with multiple robots?

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Hi,

I have two robots and they explore an unknown environment. In the second run, I want them to explore this map again but this time as a known map. How can I save the explored map in the first turn?

I tried slam_gmapping, and followed http://wiki.ros.org/slam_gmapping/Tut... tutorial. But I am not able to proceed ahead with the last step. The map-saver keeps on waiting for the map. After lots of investigations,I have the following results:

1. /map has no messages being published.
2. In the step 5 of above tutorial where we bring up slam_gmapping, I am mapping it to base_scan. But in reality I have no such topic. I have separate base_scans for each robot. /robot_0/base_scan and /robot_1/base_scan. Is there a way I can map these both.
3. I found an older post on this site, which says slam_gmapping is not possible with multiple robots. Is it still the case?
4. If slam_gmapping is not there, Is there any other way/package to save the map.

Please let me know your thoughts on this.