How to transform rtabmap/odom?

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rtabmap follows REP 103 Coordinate Frame Conventions. If you try the hand-held tutorial for Kinect v2, you will see that an optical rotation is added with a static_transform_publisher between camera_link and kinect2_link frames:

 $ rosrun tf static_transform_publisher 0 0 0 -1.5707963267948966 0 -1.5707963267948966 camera_link kinect2_link 100

then launch rgbd_odometry with _frame_id:=camera_link so that odometry is computed in ROS coordinates and not image coordinates.

Is your ground truth also in ROS coordinates? If not, you may need to add a TF to be so.

cheers