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tyrex-team / benchmarks-attitude-smartphones

Benchmark on Attitude Estimation with Smartphones (datasets & scripts)
https://tyrex.inria.fr/mobile/benchmarks-attitude
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why the norm of magnetometer calibrated isn't equal to local Earth magnetic norm #6

Closed jyzhong closed 3 weeks ago

jyzhong commented 2 months ago

https://github.com/tyrex-team/benchmarks-attitude-smartphones/blob/8ad1100294465251560723c3bfa4e823e9feed52/src/Calibration/Magnetometer/retrieveParametersFromMagnetometerCalibration.m#L22-L23

ThibaudM commented 2 months ago

I am not sure to get your question. The lines you point is the formula to apply to make calibrated magnetometer norm close to the theoretically Earth magnetic field norm.

jyzhong commented 1 month ago

Theoretically, calibrated magnetometer norm is equal to Earth magnetic field norm. Now, I calibrate my magnetometer outside, far away from magnetic disturbance, but calibrated magnetometer norm is smaller than Earth magnetic field norm. e.g. My calibrated magnetometer norm is 35uT, but local Earth magnetic field norm is 49uT. Is it means my calibration is wrong ?

ThibaudM commented 1 month ago

Which magnetometer calibration do you use?

jyzhong commented 1 month ago

@ThibaudM
I use the method about "Least Squares Ellipsoid Specific Fitting, 2004." I found another paper: Consistent least squares fitting of ellipsoids. If i should use the second because of the noise of my magnetometer ?

ThibaudM commented 1 month ago

I don't know how the "Least Squares Ellipsoid Specific Fitting, 2004." works but you can use the calibration method I used in this paper. It's based on ellipsoid fitting. You will never remove the noise of the magnetometer. With the ellipsoid fitting you will estimate the bias in the two frames: magnetometer frame and world frame.