[FieldTrip] Coordinate system conversion

[Eelke Spaak]

Dear Mohammad,

You'll need to somehow obtain a transformation matrix from the
Neuromag coordinate system into MNI space. The Neuromag coordinate
system (like any MEG subject-space coordinate system) depends on
anatomical landmarks of an invididual subject, and is thus different
for different subjects. If you have a source model in Neuromag
coordinates, apparently somehow somewhere someone had access to the
individual fiducial locations and brain anatomy. It would be worth
checking whether you can obtain this.

*Alternatively*, you could take a template MRI in MNI space and
somehow manually realign that to Neuromag space, basically treating
the template head as if it were used during the actual MEG recording.
That will give you an mni-2-neuromag transformation matrix; taking the
pinv() of that will allow you to go the other way. I'm not sure this
is wise, though. (In any case, it will be suboptimal compared to using
individual anatomy; but specifically for the volume conduction model,
I don't know whether such a linear transform messes things up.) All in
all, creating a source and head model from scratch in the appropriate
coordinate system will probably be easier.

Cheers,
Eelke

On Tue, 16 Jul 2019 at 15:42, Mohammad Ostadmohammadi
<mohammad.ostad73 at gmail.com> wrote:
>
> Yes I asked him about it, but because of large amount of data I wanted to know is there any way to convert coordinate systems without creating source_model from the scratch
>
> On Tue, Jul 16, 2019 at 6:05 PM Schoffelen, J.M. (Jan Mathijs) <jan.schoffelen at donders.ru.nl> wrote:
>>
>> You mentioned before that your supervisor provided you with the data so far. Have you asked your supervisor to help you out?
>>
>> Jan-Mathijs
>>
>>
>> On 16 Jul 2019, at 12:23, Mohammad Ostadmohammadi <mohammad.ostad73 at gmail.com> wrote:
>>
>> Hi all,
>>
>> is it possible to change source_model coordination system from neuromag to mni? i don't have access to mri data and only source_model and head_model is accessible.
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