IMU Calibration

zippyzoo777

Hello, I am working on doing some VIO SLAM with the OAK-D, and I have been having some trouble with the IMU in the unit, specifically that it is not in the neutral orientation when the camera is facing forward, which is what the SLAM expects. I was hoping I could apply a rotation matrix within the IMU calibration files (to tell the imu the orientation it should think it is in) but when I did this using the python example load calibration example, there was no change in the imu readings or their directions, no matter what I put in the IMU rotation matrix lines. (I have pasted that piece of the calibration file below, the only other thing I changed was the part of the code that chooses which calibration file to load, I changed it to the one I am trying to use.) I tried several different variations on those lines, including some utterly ridiculous matricies (like a 100.0 in every single spot) and it has no effect. The one below is what I hope to change it to. I was previously using the ros versions of things, and was able to change where it expected the IMU using the urdf files, but since I have to switch to the non-ros version of the VIO programs, I need to switch on the OAK-d as well. Has anyone experience this before or does anyone here have any ideas to fix this?

Thanks!

"imuExtrinsics": {

    "rotationMatrix": [

        [

            0\.0,

            0\.0,

            1\.0

        ],

        [

            0\.0,

            1\.0,

            0\.0

        ],

        [

            1\.0,

            0\.0,

            0\.0

        ]

    ],

jakaskerl

Hi @zippyzoo777
How about the other values? What is the value of toCamerSocket?

Thanks
Jaka

zippyzoo77

I haven't changed those at all, they are the default- all 0.0

"toCameraSocket": -1,

"translation": {

"x": 0.0,

"y": 0.0,

"z": 0.0

}

jakaskerl

Hi @zippyzoo77
It likely doesn't have an effect because the IMU extrinsincs have no reference point to anchor. Try setting the camera socket to one of your cameras the same way it is done for the camera-camera extrinsics.

Thanks,
Jaka

zippyzoo77

Ah, ok that makes sense, I will give that a try.

zippyzoo77

Alas, no luck there. I changed it to what is below. The numbers are from the models in ros, which I am assuming are the correct values, but changing the rotation matrix still had no effect on the imu output.

"toCameraSocket": 0,

"translation": {

"x": 0.0,

"y": -0.015,

"z": -0.013662

}

jakaskerl

cc @Luxonis-Adam
Any clues to the issue here? is it ROS related/is there something missing?

Thanks,
Jaka

Luxonis-Adam

Hi, by the "imu output" do you mean values coming from the IMU node? If yes, then those aren't affected by setting extrinsics as IMU node has no knowledge of the calibration, they need to be transformed with extrinsics matrix after they arrive explicitly on host

zippyzoo77

I think that's what I'm thinking of yes, I've been looking at the outputs from the IMU in the Linear_acceleration and the gyroscope_calibrated modes enabled. How would I go about doing the transformation after they arrive with extrinsics, is there a separate node for that or a different setting?

I've added the contents of the imu_gyroscope_accelerometer example to the calibration_load example and changed the raw modes to the linear-acceleration and the gyroscope-calibrated modes, that's what I'm using to see the IMU streams.