[FieldTrip] EGI 64 - channel locations doesn't work in FTrip

[Robert Oostenveld]

Hi Ana

The ft_prepare_layout function reads the electrode positions and scales them such that they fit in the sphere that represents the head.

I suggest you do 

cfg.layout = ‘yourfilename’
lay = ft_prepare_layout(cfg);

cfg = [];
cfg.layout = lay;
ft_layoutplot(cfg);

and then modify lay.pos repeatedly, every time plotting it again, until you are happy with the result. You probably want to  do this for the vertical direction 
lay.pos(:,2) = (lay.pos(:,2)+shift) .* scale;
to shift and scale the electrodes to a better fit inside/outside the sphere, and this for the horizontal
lay.pos(:,1) = lay.pos(:,1) .* scale;
as they seem to be properly centred along the x-axis alreadly.

After this, you can 
save yourlayout.mat lay
and specify “yourlayout.mat” as the layout filename for your future figures.


best regards
Robert



On 12 May 2015, at 10:17, Anna Wieczorek-Taraday <anna.wieczorek.taraday at gmail.com> wrote:

> Dear Fieldtrippers, 
> 
> I have a problem while reading EEG (EGI) electrode location file to FieldTrip.
> I am using EGI Amp 300, 64-channel cap, data were exported to .raw files.
> 
> When I read locations to EEGLAB, it works well  (lilnk to pictures || see pic. eeglab_chanlocs.jpg). The layout corresponds with the actual electrode placement in the cap.
> When I read the same file into FieldTrip, the electrodes seem to have similar layout (see pic. fieldtrip_chanlocs.jpg). 
> However, it seems like the electrodes are confined within the plot too much. Electrodes E61:E64 should be outside of boundaries of the layout plot.
> 
> I was wondering whether anybody else had similar issue and did overcome it? Could anybody suggest what is wrong and how can I read the locations properly?
> Any support will be appreciated.
> 
> I am using Matlab 2015, eeglab eeglab13_4_4b and the latest version of fieldtrip.
> 
> ***************************************
> 
> 
> Here is code I used to read these locations:
> 
> cfg.layout      = 'C:\Users\annwie\Documents\awt_chanlocs\GSN-HydroCel_64.sfp'; 
> cfg.feedback    = 'yes';
> layout          = ft_prepare_layout(cfg);
> 
> 
> Here is the code that I used to preprocess my data in Fieldtrip:
> 
> cfg = [];
> cfg.trialfun = 'ft_trialfun_general';
> cfg.dataset = '136.set';
> cfg.trialdef.eventtype  = 'trigger';
> cfg.trialdef.eventvalue = 'DIN8'
> cfg.trialdef.prestim    = 0.5;
> cfg.trialdef.poststim   = 2.5;
> cfg = ft_definetrial(cfg);
> 
> cfg.lpfilter = 'no';
> cfg.hpfilter = 'yes';
> cfg.hpfreq = 0.3;
> data = ft_preprocessing(cfg);
> 
> Anna Wieczorek-Taraday.
> 
> PhD Student   
> Nencki Institute of Experimental Biology
> Pasteur Street 3, 02-093 Warsaw, Poland
> 
> Warsaw University of Social Sciences and Humanities
> Chodakowska Street 19/31, 03-815 Warsaw, Poland
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip

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