[Mne_analysis] question about FIFF constants and CTF data

[Denis A. Engemann]

Hi all,

> On Jun 26, 2014, at 11:29 PM, dgw <dgwakeman at gmail.com> wrote:
> 
> 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).

Lists are ordered, dictionaries aren't.

> It seems that in the case of the file you are talking about, you get three HPI locations and 2 EEG locations.
> 

IIRC you normally get 3 fiducials followed by 2 hpi coils

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

good idea :-)

> 
> 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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