KIT data doesn't retain MAG/GRAD type for channels

[monkeyman192]

When importing KIT data we noticed that although the channel type is correct in the channel data (6001 for KIT data: FIFF.FIFFV_COIL_KIT_GRAD (we have gradiometers)), when observing the info of the raw we get chs : list | 193 items (MAG: 125, MISC: 67, STIM: 1)
Looking through the reason for this, it is because both MAG and GRAD type sensors are given FIFF.FIFF_UNIT_T as their unit, but when the channel type is determine by pick.py, the GRAD channel type has the FIFF.FIFF_UNIT_T_M type, so KIT data will never be realised to be a GRAD channel.
It is simple to add a few lines in the kit.py file to check whether the channel type is a gradiometer or magnetometer and set the units appropriately.
If this seems reasonable I can make a PR with the changes (unless there is a better way?)

[agramfort]

@monkeyman192 : axial gradiometers like CTF with systems are considered by MNE as magnetometers on purpose. It's because they produce data that are much closer to a magnetometer as to a planer gradiometers in a vectorview system.

does it help?

[monkeyman192]

Ah, ok, I see.
This still leaves an issue that when being used in conjunction with mne-bids the channel type in the channel tsv is listed as a magnetometer channel, whereas it should be listed as an axial gradiometer. This can probably be fixed on the mne-bids end though by being a bit more thorough when checking the channel type...

[agramfort]

agreed. Can you open an issue / PR in the mne-bids repo?

[jasmainak]

yes, please let's discuss on mne-bids

[larsoner]

Closing as non-MNE issue but feel free to reopen if there is something we need to do here