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Hi!
I'm trying to reposition the opm sensors from the mne opm tutorial using
BEM outer skin coordinates but end up placing the senors inside the brain.
How should the BEM coordinates be transformed in order for these
coordinates systems to align?
Best,
Karin
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Karin,
You have to be careful following the OPM example
<https://mne.tools/dev/auto_examples/datasets/plot_opm_data.html>, see the
note from it:
The Head<->MRI transform is an identity matrix, as the co-registration
method used equates the two coordinate systems. This mis-defines the head
coordinate system (which should be based on the LPA, Nasion, and RPA) but
should be fine for these analyses.
The BEM in MNE is in MRI (freesurfer surface RAS) coordinates as defined by
the Freesurfer reconstruction. This example and related documentation might
help you sort out what you are trying to do: