Multi-Mapping with rtabmap , how to?

Posted by alexr on
URL: http://official-rtab-map-forum.206.s1.nabble.com/Multi-Mapping-with-rtabmap-how-to-tp202.html

Dear Mathieu,

I have finished the tutorial from the RTABMAP multi-session mapping using the standalone rtabmap.
I want to create something similar to that tutorial using ROS and rtabmap on my robot platform.
I am so far able to produce nice maps, but due to limitation on the memory, I would like to try large scale mapping(eg. mapping the entire ground floor of a buildiing).

My system consists of a robot platform with a URG hokuyo senor and xtion pro live sensor. I get fairly good odometry from my robot. I am using ROS hydro.  My questions are:

1) From the video, there are 5 databases that are run one after the other once each one finishes mapping. To do that, do I need to save each database by killing rtabmap launch so that it stores the rtabmap.db in default .ros/rtabmap.db, then, save this file to some place as map1. And then, continue mapping by repeating this process of killing the node and saving. Can you provide details on how you created the databases?

2) From the multi-session mapping tutorial, I see that when the second database is selected  the process starts with a new origin and the previous data vanishes. As rtabmap finds the earlier visited areas that part of the visited map is added to the present map, am I correct on this part? How does the trajectory adjusts, as i can see from the final graph map the graph nodes and trajectory is smooth with just one origin? How do rtabmap deals with multiple graph trajectories to generate a single smooth trajectory with edges and vertices?

4) If I remove "delete_db_on_start" from the launch file, will the rtabmap continue to map from the previous mapping session? How is this method different from the multi-session mapping apart from it will create a single database?

5) Also, when viewing the process in rviz, how do I visualize the graph nodes with edges and vertices as can be seen in the standalone rtabmapviz?

Sorry for too many questions.

Thank you
Alex