[Mne_analysis] question about FIFF constants and CTF data

[dgw]

Hi Gustavo,

I'm not entirely sure what your question is, but I can tell you this. I
don't think lists are ordered in python (and raw.info['dig'] is a list). It
seems that in the case of the file you are talking about, you get three HPI
locations and 2 EEG locations.

Are you asking why aren't there fiducial points? If so can you tell us more
about the data, were these points digitized?

Thanks,
D



On Thu, Jun 26, 2014 at 4:00 PM, Gustavo Sudre <gsudre at gmail.com> wrote:

> hey all
>
> I'm working with CTF data after converting them to FIFF. I used a simple
> mne_ctf2fiff call, and my data has no digitized points nor EEG. After
> looking at raw.info['dig'] I was a bit unsure about the location of the 3
> electrodes that were used (LPA, RPA, nasion), so I decided to check a
> sample dataset just to verify it wasn't something weird with my data.
>
> So, I converted Brainstorm's sample raw .ds to FIFF (sorry, I didn't find
> a sample .ds by the MNE-python gang ;) ), and looked at the dig structure.
> Here's what I see:
>
> In [8]: raw.info['dig']
> Out[8]:
> [{'coord_frame': 4,
>   'ident': 3,
>   'kind': 2,
>   'r': array([  7.45058060e-09,   8.64083171e-02,   0.00000000e+00],
> dtype=float32)},
>  {'coord_frame': 4,
>   'ident': 1,
>   'kind': 2,
>   'r': array([ -6.84481487e-02,  -5.76255843e-09,   0.00000000e+00],
> dtype=float32)},
>  {'coord_frame': 4,
>   'ident': 2,
>   'kind': 2,
>   'r': array([  7.05333501e-02,   5.87897375e-09,   0.00000000e+00],
> dtype=float32)},
>  {'coord_frame': 4,
>   'ident': 1,
>   'kind': 3,
>   'r': array([-0.02922045, -0.09704589,  0.0735818 ], dtype=float32)},
>  {'coord_frame': 4,
>   'ident': 2,
>   'kind': 3,
>   'r': array([ 0.03363838, -0.09628744,  0.0735818 ], dtype=float32)}]
>
> The two last points are not present in my actual data, but the output
> above can be used to illustrate my question. Based on the coordinates in
> head space, shouldn't the first point be nasion (FIFFV_POINT_NASION,
> ident=2)?
>
> Maybe I'm misreading something in the manual, but it's something that has
> been bugging me for a while, and I was wondering if you guys could quickly
> point out my mistake!
>
> Thanks,
>
> G
>
>
> --
> Gustavo Sudre
>
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