[Mne_analysis] BEM coordinate frame?

[Eric Larson]

        External Email - Use Caution        

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:

-
https://mne.tools/stable/auto_tutorials/source-modeling/plot_source_alignment.html
-
https://mne.tools/dev/overview/implementation.html#meg-eeg-and-mri-coordinate-systems

plot_alignment <https://mne.tools/dev/generated/mne.viz.plot_alignment.html>
is what I always use to make sure everything is coregistered properly.

Eric


On Sun, Jan 19, 2020 at 3:47 PM Karin Westin <karin.westin85 at gmail.com>
wrote:

>         External Email - Use Caution
>
> 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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