{"action":"created","issue":{"url":"https://api.github.com/repos/googlecartographer/cartographer_ros/issues/809","repository_url":"https://api.github.com/repos/googlecartographer/cartographer_ros","labels_url":"https://api.github.com/repos/googlecartographer/cartographer_ros/issues/809/labels{/name}","comments_url":"https://api.github.com/repos/googlecartographer/cartographer_ros/issues/809/comments","events_url":"https://api.github.com/repos/googlecartographer/cartographer_ros/issues/809/events","html_url":"https://github.com/googlecartographer/cartographer_ros/issues/809","id":311625453,"number":809,"title":"z position drift during front end slam","user":{"login":"slamer-run","id":7335808,"avatar_url":"https://avatars0.githubusercontent.com/u/7335808?v=4","gravatar_id":"","url":"https://api.github.com/users/slamer-run","html_url":"https://github.com/slamer-run","followers_url":"https://api.github.com/users/slamer-run/followers","following_url":"https://api.github.com/users/slamer-run/following{/other_user}","gists_url":"https://api.github.com/users/slamer-run/gists{/gist_id}","starred_url":"https://api.github.com/users/slamer-run/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/slamer-run/subscriptions","organizations_url":"https://api.github.com/users/slamer-run/orgs","repos_url":"https://api.github.com/users/slamer-run/repos","events_url":"https://api.github.com/users/slamer-run/events{/privacy}","received_events_url":"https://api.github.com/users/slamer-run/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":5,"created_at":"2018-04-05T14:07:07Z","updated_at":"2018-04-06T08:06:44Z","closed_at":null,"author_association":"NONE","body":"With 3d cartographer with single Lidar and IMU, z position have negligible drift at front end slam.  Even if the robot doesn't move at all, the z position drift more than 1 m in a few minutes. \r\n\r\n- launch: https://github.com/googlecartographer/cartographer_ros/blob/master/cartographer_ros/launch/demo_backpack_3d.launch\r\n\r\n- lua: https://github.com/googlecartographer/cartographer_ros/blob/master/cartographer_ros/configuration_files/backpack_3d.lua\r\nThe only one parameter is changed as following. \r\nbefore: num_point_clouds = 2\r\nafter: num_point_clouds = 1\r\n\r\n- rosbag & urdf: Sorry, but I can't upload rosbag for some reasons. The tested rosbag is validated, though   \r\n\r\nShould I add barometric sensor in order to suppress z position drift at front end slam? Or, Is it necessary to have double lidar to use 3d cartographer slam?\r\n\r\nThanks in advance. \r\n"},"comment":{"url":"https://api.github.com/repos/googlecartographer/cartographer_ros/issues/comments/379180142","html_url":"https://github.com/googlecartographer/cartographer_ros/issues/809#issuecomment-379180142","issue_url":"https://api.github.com/repos/googlecartographer/cartographer_ros/issues/809","id":379180142,"user":{"login":"gaschler","id":339437,"avatar_url":"https://avatars3.githubusercontent.com/u/339437?v=4","gravatar_id":"","url":"https://api.github.com/users/gaschler","html_url":"https://github.com/gaschler","followers_url":"https://api.github.com/users/gaschler/followers","following_url":"https://api.github.com/users/gaschler/following{/other_user}","gists_url":"https://api.github.com/users/gaschler/gists{/gist_id}","starred_url":"https://api.github.com/users/gaschler/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/gaschler/subscriptions","organizations_url":"https://api.github.com/users/gaschler/orgs","repos_url":"https://api.github.com/users/gaschler/repos","events_url":"https://api.github.com/users/gaschler/events{/privacy}","received_events_url":"https://api.github.com/users/gaschler/received_events","type":"User","site_admin":false},"created_at":"2018-04-06T08:06:44Z","updated_at":"2018-04-06T08:06:44Z","author_association":"CONTRIBUTOR","body":"> You meant if Lidar can see the ground, can it result in constraint for z position, pitch and roll estimation?\r\n> What is more, 3d cartographer slam can consider ground plane as important factor? \r\n\r\nNo, it treats \"ground\" like any other point cloud. I just wanted to rule out the case that you only see walls because that would be an obvious reason for drift.\r\n\r\n> the tilt of all submaps built when driving on this slope will depend on the pitch your IMU \r\n\r\nThanks @ojura for this excellent explanation. I also believe this is the reason.\r\n"}}
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