channel locations

Vladimir Litvak v.litvak at ION.UCL.AC.UK
Wed Jun 24 10:36:45 CEST 2009


On Wed, Jun 24, 2009 at 8:42 AM, peng wang<prion.w at gmail.com> wrote:
> Thank you, Vladimir.
> Does that mean I can get the coil position by the equation below; and ignore the "ori" information?
> position = data.grad.tra*data.grad. pnt;

No. grad.tra is about combining sensor signals to get channel signals,
not about combining positions. If you want to get a single locations
per channel (for instance for topoplotting) you can use the function
'channelposition'. 'ori' is a different way to represent the same
information as in grad.tra. It is used for some MEG systems.

Best,

Vladimir


>
> Best
> Peng
> =========
> Dear Peng,
>
> These are the real locations. Each channel in your MEG data is
> computed by combining signals from several magnetometer coils (usually
> two). The locations of these coils are given in grad.pnt and the way
> they are combined is described by grad.tra.
>
> Best,
>
> Vladimir
>
> On Tue, Jun 23, 2009 at 8:03 PM, peng wang<prion.w at gmail.com> wrote:
>> Dear list members,
>>
>>        I am a new user of fieldtrip. I have some data preprocessed by fieldtrip. I want to find the channel location information from the field 'grad' in the dataset after this procedure. The original channel number should be 303, but in this field , it looks like this:
>>          pnt:  [597*3];
>>          ori:  [597*3];
>>          tra:  [303*597];
>>        label:  {303*1 cell}
>>         unit:  'cm'
>>  balance:  {1*1 struct}
>>
>> It seemed there were some transformations(303->597). How did this happen? How can I retrieve the real location information of the sensors?Thank you very much for help!
>>
>> peng
>>
>> ----------------------------------
>> The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.
>>
>>
>
> ----------------------------------
> The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.
>
>

----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.



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