How RTAB-Map find the point cloud gravity direction?

Posted by Jacky Liu on
URL: http://official-rtab-map-forum.206.s1.nabble.com/How-RTAB-Map-find-the-point-cloud-gravity-direction-tp3661.html

After installing rtab-map ros and run on real environment, I found that rtab-map could plot the point cloud in ros rviz with correct gravity direction.  How does it do that?  Could someone give me the section of paper or code which describe the related method?