When IMU is rotated, accelerations are not correctly calculated

[jpgarduino]

Iim using an Intel RealSense D435i on ROS2 Humble. If the IMU is mounted with no rotations (in the URDF rpy = "0 0 0") orietantion is correctly calculated in the filter. But if IMU is mounted with rotations, the result orientation is not correct.

In fact, with the following rotation configuration:

<joint name="camera_base_joint" type="fixed"> <parent link="base_link"/> <child link="camera_link"/> <origin xyz="0.73878 0.2785 0.1794" rpy="1.364 -0.134390 0.628319"/> </joint>

IMU message is the following one:

` root@AMR:/home/debix# ros2 topic echo /camera/camera/imu --once
header:
stamp:
sec: 1760639159
nanosec: 875420672
frame_id: camera_imu_optical_frame
orientation:
x: 0.0
y: 0.0
z: 0.0
w: 0.0
orientation_covariance:

• -1.0
• 0.0
• 0.0
• 0.0
• 0.0
• 0.0
• 0.0
• 0.0
• 0.0
  angular_velocity:
  x: 0.0
  y: 0.003490658476948738
  z: -0.001745329238474369
  angular_velocity_covariance:
• 0.01
• 0.0
• 0.0
• 0.0
• 0.01
• 0.0
• 0.0
• 0.0
• 0.01
  linear_acceleration:
  x: -9.316317558288574
  y: -0.6472389101982117
  z: 2.1378495693206787
  linear_acceleration_covariance:
• 0.01
• 0.0
• 0.0
• 0.0
• 0.01
• 0.0
• 0.0
• 0.0
• 0.01
  ---`

and the results accelerations are not correct. After making a lot of test, I found a solution: adding a new node that republish the IMU message but converting all data to the base_link frame. With this change, it seems the orientation is now correctly.

Since already exists a TF from "camera_imu_optical_frame" to "base_link", and the added node is only using this tranform to convert the data:

• Why is this node needed?
• Is it possible to do it directly without converting before the IMU message?