IMU Magnetometer CALIBRATED output

PriyaJakhar28

Hi, I would like to what all factors is the magnetometer output calibrated for when I use CALIBRATED output. The raw readings are in the 1000s while the calibrated output is somewhere up to 100 for me depending on the location I use it.

jakaskerl

Hi PriyaJakhar28
According to the BNO085 datasheet (https://www.ceva-dsp.com/wp-content/uploads/2019/10/BNO080_085-Datasheet.pdf):

Magnetic Field Calibrated (in μTesla)

Fully Calibrated: This output has undergone corrections for both soft-iron and hard-iron distortions.
Absolute Orientation: Used to determine the sensor's absolute orientation with respect to magnetic north.
Accuracy Field: An indicator provided to show the degree of calibration, useful for understanding the reliability of the readings.

Magnetic Field Uncalibrated (in μTesla)

Hard-Iron Offset Not Applied: This is the raw magnetic field measurement without the hard-iron offset.
Separate Hard-Iron Estimate: The hard-iron offset is provided as a separate parameter, allowing for manual application if needed.

Raw Magnetic Field Measurement (in ADC units)

Direct Data: This is the raw, unprocessed data directly from the magnetometer.
Testing: Primarily used for testing purposes to understand the raw capabilities of the sensor.

Soft-Iron and Hard-Iron Effects

Soft-Iron Effect: Distortions caused by materials that can temporarily become magnetized.
Hard-Iron Effect: Distortions caused by constant magnetic fields in the environment.
Calibration Movement: To remove these distortions, the device must be moved sufficiently through all three axes (X, Y, Z) of 3-dimensional space.

Hope this helps,
Jaka

PriyaJakhar28

Is there a way to query for the matrices that compensate for soft and hard iron offsets? Also is there an explanation for why the raw measurements are so high when the unit is uT?

jakaskerl

Hi PriyaJakhar28
I think that would be a question for the makers of BNO085; this info in not publicly available I think.
Raw measurements should be ADC units as per manual. Perhaps this explains the range of values reported.

Thanks,
Jaka

PriyaJakhar28

Hi, I would suggest to update the documentation on Luxonis site to reflect that the raw measurements are in ADC units and not uT. Also if the calibration stats are not publicly available, does that mean that you guys haven't changed it? I was just trying to find out if the magnetometer has been calibrated for the camera casing.

jakaskerl

Hi PriyaJakhar28
Hm, I'll ask the firmware team on this.
And there is likely a mistake in the docs. I'll fix that if that's the case.

EDIT: values were taken directly from IMU without postprocessing, except for RAW accelerometer and gyroscope. Those are decoded ADC values.

Thanks,
Jaka