Merge local grid maps of multi-session mapping

Posted by ChristianF on
URL: http://official-rtab-map-forum.206.s1.nabble.com/Merge-local-grid-maps-of-multi-session-mapping-tp7102.html

We have a large facility I want to map in stages. I've already created a decent map of a large portion of the facility but need to add additional rooms/corridors. I am able to continue mapping by starting on the existing map in localization mode, going to where I want to extend the map, setting mapping mode, and then going into the unknown (as recommended for multi-session mapping). This works but after a little while the occupancy grid map published on /rtabmap/grid_map is replaced by a new map that only shows the newly explored area. I understand from reading in this forum that this is expected, and that the old map may reappear on that topic when the robot is back in that old area and a loop closure is detected. But I still need the complete map for navigation.

Q1: Is there a way to ask rtabmap to publish the global, merged 2D map during localization mode?

Q2: Alternatively, is there a way to export the merged 2D map? I finally figured out how to export each individual map (database viewer > select the node in the graph view (this step wasn't obvious) > Regenerate optimized 2D map > Export optimized 2D map). So that's a starts, but these maps come without a yaml file containing the origin, so it's not clear how to align them for merging.

Thanks for your help!