[Mne_analysis] Help with DigMontage coordinates for EGI system

[Kadwani, Manorama]

Hi all,

I am using MNE v0.20 and trying to read electrode locations from an EGI system in .xml file format.

For this purpose, I used the function "mne.channels.read_dig_egi". Whereas, my colleague has previously used "mne.channels.read_dig_montage" which is now discontinued in versions after v0.18. Both the functions return a DigMontage instance with a list of electrode number and their locations. Our issue is that the two montages have the locations with different values and different units; read_dig_egi uses 'mm' and read_dig_montage uses meters. Simply scaling is not enough as even then the numbers are different. Any ideas on why the two montages are different for the same EGI file?

Another issue related to the coordinates: While aligning the EEG/MRI coordinates, my sensor points are way off from the head model. The points are invisible even after marking fiducials. ICL alignment does not work and gives an error that there was too large difference in matching. But when my colleague used the older function "read_dig_montage", the sensor points were visible and also aligned well to the head model.

Let me know if I should provide more information. I have attached the two montage files, if that would be of any help.

Thanks,
Manorama Kadwani
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