[Mne_analysis] Digitization data for new Polhemus system

[Teon Brooks]

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Hi Emily,

We don't have a way to read the native file from FastScan in MNE. However,
we do support data exported as text files. I don't have the software handy
but there should be a way to export the surface points, electrode points,
and the fiducials, all as separate text files. We based this off the
routine we used for the KIT-NYU lab where we bundled the electrode points
and the fiducials in the same file export.

For creating the DigMontage, we have a function `read_dig_montage` that
takes these text files as input.
- The HPI are the marker points that your MEG system generate in the native
MEG space
- The ELP are those same points that are digitized in the native FastScan
space with the addition of the fiducials, which are in the same native
FastScan space.
- The point names are labels for the markers and then the name of the
fiducials (nasion, lpa, rpa) in their respective order from the ELP file.

Please follow up if you have any more questions about this and how we might
make it more accompanying for other lab setups.

HTH,

On Wed, May 16, 2018 at 1:17 PM Emily Stephen <emilyps14 at gmail.com> wrote:

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>
> Hi All,
>
> My lab has started using a new *Polhemus FastScan II* system to get the
> digitization data (head shape points, electrode position points,
> fiducials). The scanner itself doesn't identify or output the points: it
> returns a 3d head surface image, from which we'll need to extract the
> electrode positions, etc. We are working on a tool to label the points
> manually and output them in a format that we can use in MNE to create a
> DigMontage.
>
> (1) Has anyone used this system before with MNE? We'd rather not re-invent
> the wheel if we don't have to.
> (2) If not, is there a spec or detailed description of (a) the point
> definitions and (b) digitizer file formats, that we could use as a basis
> for the outputs of our tool?
> (3) Any other advice for us or pitfalls that we should watch out for?
>
> Thanks,
> Emily
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-- 
teon <http://www.twitter.com/teon_io>, phd
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