Realsense-ros: Intel t265: where is IMU frame?

[PerrineAguiar]

Hi,

In which frame is supposed to be expressed the raw IMU data?

Regarding the orientation, none of the frames published by the driver seems to correspond to the actual IMU frame. I would expect that camera_accel_frame or camera_accel_optical_frame should be the one, but looking at the raw IMU data, the actual IMU frame should have: x pointing forward, y pointing right and z pointing down.

Regarding the position, is the IMU located at the origin of the camera_accel_frame or at the origin of the camera_pose_frame?

Thanks in advance.

[schmidtp1]

Hi @PerrineAguiar,

The raw sensor readings are expressed in the camera_accel_optical_frame but then transformed: https://github.com/IntelRealSense/realsense-ros/blob/development/realsense2_camera/src/base_realsense_node.cpp#L1245
In case the target frame should be camera_accel_frame, the rotation matrix (to transform from optical frame to frame) should be [0 0 1; -1 0 0; 0 -1 0].
Personally, I think the data should just be expressed in the original frame.

The origin of the IMU is located at camera_accel_frame. (The camera_pose_frame is centered between the two fisheye.)

[PerrineAguiar]

@schmidtp1 thanks for the quick answer.
Regarding the orientation, there might be a bug. If I look at the the camera_accel_frame and the camera_accel_optical_frame in rviz, it looks like the conversion function should be something like:

void BaseRealSenseNode::ConvertFromOpticalFrameToFrame(float3& data)
{
    float3 temp;
    temp.x = -data.z;
    temp.y = -data.x;
    temp.z = data.y;

    data.x = temp.x;
    data.y = temp.y;
    data.z = temp.z;
}

[doronhi]

@PerrineAguiar
I think you may be right and there is a problem with that code. The solution, however, is not just fixing the function as you say, since it is also used by D435i.
I am working on it these days.

[doronhi]

Fixed in #778 .
I agree with @schmidtp1 , removed the function ConvertFromOpticalFrameToFrame and changed the frame_id to be in the original coordinate system, as described in the _optical_frame.