About the Imu data

[Liulong Ma]

Hi, I pay attention to that in kitti2bag.py, imu message is assigned as

        imu.linear_acceleration.x = oxts.packet.af
        imu.linear_acceleration.y = oxts.packet.al
        imu.linear_acceleration.z = oxts.packet.au
        imu.angular_velocity.x = oxts.packet.wf
        imu.angular_velocity.y = oxts.packet.wl
        imu.angular_velocity.z = oxts.packet.wu

But in the definition of kitti raw_data:

af: forward acceleration (m/s^2).
al: leftward acceleration (m/s^2).
au: upward acceleration (m/s^2).
wf: angular rate around forward axis (rad/s).
wl: angular rate around leftward axis (rad/s).
wu: angular rate around upward axis (rad/s).

That is the absolute values, but IMU measures the relative acceleration and angular rate in its coordinate. Why doesn't use the following values?

ax: acceleration in x, i.e. in direction of vehicle front (m/s^2).
ay: acceleration in y, i.e. in direction of vehicle left (m/s^2).
ay: acceleration in z, i.e. in direction of vehicle top (m/s^2).
wx: angular rate around x (rad/s).
wy: angular rate around y (rad/s).
wz: angular rate around z (rad/s).

[Liulong Ma]

In the KITTI paper：

Accelerations and angular rates are both specified using two coordinate systems, one which is attached to the vehicle body(x, y, z)and one that is mapped to the tangent plane of the earth surface at that location(f, l, u).

[Marc Haubenstock]

This is fine. It is the correct coordinate system to export. Your second comment refers to gps vs rest.

[Liulong Ma]

@geoeo sorry, do you mean the original assignment is right？ how to explain my fist comment？

[Marc Haubenstock]

I see your point. I think it should be x,y,z as well. Practically however, I tried a motion integration with both and it didnt make any difference. But for completeness it should be x,y,z

[Liulong Ma]

@geoeo and for my second comment, in the paper it refers both gps and IMU:

OXTS (GPS/IMU):For each frame, we store30differ-ent GPS/IMU values in a text file: The geographic coordinatesincluding altitude, global orientation, velocities, accelerations,angular rates, accuracies and satellite information. Accelerations and angular rates are both specified using two coordinatesystems, one which is attached to the vehicle body(x,y,z)andone that is mapped to the tangent plane of the earth surfaceat that location(f,l,u).

[hb]

I see your point. I think it should be x,y,z as well. Practically however, I tried a motion integration with both and it didnt make any difference. But for completeness it should be x,y,z

Hi, can I ask you how you got the same trajectory with motion integration using both xyz and flu?
For FLU what motion integration equation did you used?
Thank you.