Biosemi64 montage and Nz as tip-of-nose

Describe the problem

I use biosemi to record 64 electrodes with two additional electrodes: cheek and tip of the nose (as Nz). Previously, I loaded and applied the built-in montage: montage = mne.channels.read_montage('biosemi64', unit='mm', transform=True) raw.set_montage(montage, set_dig=True) It just informed me that cheek is not part of the biosemi64 montage and thus gets no position.

With the new DigMontage changes, I try using: montage = mne.channels.make_standard_montage('biosemi64') raw.set_montage(montage)

I get this error: ValueError: DigMontage is a only a subset of info. There are 2 channel positions not present in the DigMontage. The required channels are: [‘Nz’, ‘Cheek’]

After removing Cheek, I still get an error for Nz which should be a part of the biosemi64 montage. Only by removing both cheek and Nz the montage works.

Describe your solution

I want to be able to apply the biosemi64 montage to the electrodes that match the default montage and maybe provide additional positions for my other electrodes.

I realize that Nz is a fiducial and should not be used for the tip of the nose. However, its position is not important for its purpose as a reference later. The cheek is used to create a virtual eog channel (Fpz - cheek) and is deleted after preprocessing.

Describe possible alternatives

Add a description to the documentation how this can be done. I’m sure its a usual thing.

Additional context

Add any other context or screenshots about the feature request here.

[agramfort]

@Eklund89 you can do this:

import mne
file = "sample_raw.fif"
raw = mne.io.read_raw_fif(file)
montage = mne.channels.make_standard_montage('biosemi64')
raw.set_channel_types({'Nz': 'misc', 'Cheek': 'misc'})
raw.set_montage(montage)

basically we need to know the position of all EEG channels to set the montage. biosemi64 does not contain location for Nz or Cheek.

HTH

[cbrnr]

@Eklund89 I’m closing for now because we’ve provided some potential answers to your question. Feel free to re-open, or better yet, ask on our mailing list or Gitter channel because this is more a usage question.