[Eeglablist] chan locs file generation

[arno]

Dear Sim,


> Can anyone help me how eeglab takes into account the electrode 
> positions. How the chan locs file (.txt) is generated for 10 -20 
> system and how the cartesian coordinates are calculated. Can I 
> generate a chan locs file for a grid like 4*4 with 16 channels etc.
>
Yes, this is possible. The channel location structure is described at

http://www.sccn.ucsd.edu/eeglab/structtut/datastruct.html#EEG.chanlocs:

You have the option 'plotgrid' of topoplot or
to generate a grid in EEGLAB, do something like this

% generate coordinates
count = 1;
for x = -1:4:1
   for y = -1:4:1
      [EEG.chanlocs(count).theta EEG.chanlocs(count).radius] = 
cart2pol(x,y); % convert to planar polar
      EEG.chanlocs(count).labels = sprintf('Elec %d', count);
      count = count+1;
   end
end

% convert to other formats
EEG.chanlocs = convertlocs(EEG.chanlocs, 'topo2all');

Then topoplot has an option to mask the head ('headrad', 0)

Hope this helps,

Arno