[Eeglablist] Biosemi 128 electrode channel locations

[Cedric Cannard]

Hi Omar,

I encountered this "issue" a long time ago.

1) Download the excel file with electrode coordinates from the website: https://urldefense.com/v3/__https://www.biosemi.com/headcap.htm__;!!Mih3wA!DPWeDcP7O-lYLFgClhv-S93Qh06tkiAjl6X7kR5UfhdlPZRkaxYcBH2jumBinHo9a2ls5BVbkgT_RVUtlG8mm_5dGQ$ 
(click on the box "Download the position coordinates of the standard BioSemi headcaps") next to the 2nd table
2) go to the 128 electrodes tab
3) make yourself a script that loads the column X, Y, Z, sph_theta, sph_phi and create the EEGLAB compatible EEG.chanlocs structure. Something like:

tbl = readable('path_to_table_you_downloaded_on_your_computer/Cap_coords_all.xlsx');

% keep only rows of interest
tbl(1:34,:) = []; % remove first 34 rows

for elec = 1:128
   chanlocs(elec).labels = tbl{1,elec};  % electrode label
   chanlocs(elec).X = tbl{5,elec};       % X coordinate
   chanlocs(elec).Y = tbl{6,elec};       % Y coordinate
   chanlocs(elec).Z = tbl{7,elec};       % Z coordinate
   chanlocs(elec).sph_theta = tbl{11,elec};       % spherical theta
   chanlocs(elec).sph_phi = tbl{12,elec};       % spherical phi
end

% check and overwrite current EEGLAB chaloncs structure
EEG.chanlocs = chanlocs;
clear chanlocs

% Check
EEG = eeg_checkset(EEG);


This is from memory as an example, so please check everything and play with it, ensure labels match the order, etc. or ask your favorite LLM to do it for you, this kind of task should be pretty simple for them.

You can replace the config file in the Actiview Software for next times so you don't have to do the conversion. I believe this is discussed on the Biosemi website or forum.

Hope this helps,

Cedric Cannard



On Tuesday, September 16th, 2025 at 10:36 AM, Omar Rodriguez via eeglablist <eeglablist at sccn.ucsd.edu> wrote:

> Hi all,
>
> I am having issues with importing the channel locations of a BioSemi 128 electode system. This system follows non-standard naming (ABC), and thus the loc/sfp/elp files in eeglab do not work for my system, even if I rename the electrodes.
>
> I imported my own XYZ coordinates in a .sfp file, but eeglab GUI does not put them in their correct boxes (will put the Y value in the X box, and put a -X value in the Y box). The best I have done is in the photo below - but there are several electrodes outside the scalp when they should be in.
>
> [cid:e191eb85-abab-4caf-b6e1-c3728bdf5d1a]
>
> Does anyone have a similar experience and/or solution?
>
> Thank you!!
>
> Omar Rodriguez
> Neuroscience Graduate Program | Florida Atlantic University
> Neuroscience, B.S | Baylor University
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