Question about IMU information usage

[jacklu333333]

In the rtabmap, it does subscribe to the IMU information. I wonder how is the information being utilized. I couldn't find detailed information about it.
Does the rtabmap only use the orientation information inside the IMU topic? Or it will use the linear acceleration and angular acceleration information as well?

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Because in my case, I add an additional inertial sensor for my robot. Due to the fact that my robot base only has the gyroscope(without accelerometer). I refer to some of the examples of merging inertial sensor information from here.  Hence, I use madgwick filter to obtain the orientation data for the additional IMU sensor. However, without magnetic, the yaw would be randomly initialized, and with a magnetic sensor, it would provide absolute orientation.

Hope someone can help me.
Best Regards,
Jack Lu

[matlabbe]

Hi,

rtabmap requires the IMU quaternion (so yes only orientation) computed by madgwick or complementary filters (or imu directly if the imu provides already the quaternion). Here are some cases:

With gyroscope only, orientation will drift in roll, pitch and yaw over time. Can be still useful to track fast change in rotation for rtabmap's odometry nodes to guess next odometry transform (in particular for ICP odometry), but should not be used with rtabmap node, which uses it as gravity constraints in the map's graph (i.e., pitch and roll should not drift!).

With accelerometer only, orientation won't drift in roll and pitch, but in yaw over time. However, orientation changes may not be tracked accurately.

With accelerometer and gyroscope (6DoF IMU), the orientation won't drift in pitch and roll, but in yaw over time. The change of orientation will be more accurate than using accelerometer alone though. This is the recommended minimal setup for rtabmap.

With accelerometer, gyroscope and magnetometer (9DoF IMU), then you have absolute orientation in roll, pitch, yaw (based on North). This setup is sensitive to magnetic fields though, in some cases (e.g., indoor) it adds more error in yaw though, so I prefer using 6DoF IMU indoor.

cheers,
Mathieu