I’ve got .fif files with meg and eeg data. I want to localize eeg and meg sources separately and eeg+meg together. With meg I use -trans file which is obtained after co-registration, and I want use it for eeg too, but everything is different in this tutorial EEG source localization given electrode locations on an MRI — MNE 1.5.0 documentation
Do I need dig_montage for eeg, if i have a -trans.fif file after coregistration? And what are the main differences between meg and eeg localization, excluding the 3-layer bem? And what should be considered for MEG+EEG localization?
yes, your MEG and EEG coregistration is separate from each other in the sense that MEG and EEG coordinate space are most likely separate from each other in your data set.
Coregistration is an important concept to grasp for source reconstruction - and an important step to get right for the goodness of fit of your source solution.
Explaining the details here is probably a bit beyond (at least my) scope as it is not easily described in two sentences, but maybe you can ask someone to explain it to you?
If you do not have the resources available around you, you can also search for education material online - e.g. there is a talk about source reconstruction by me from PracticalMEEG 2022 that is online on Youtube (and you might find other talks online as well).