[Eeglablist] About electrode locations (Easycap) and topoplot

[AI KOUITSU]

Hello all,

 I am a beginner, and I have some questions about how to calculate
the electrode locations for Easycap and the topoplot() function.

1. As is written in this page http://sccn.ucsd.edu/wiki/Channel_Location_Files,
the Easycap electrode location file seems compatible with eeglab-->readlocs() 
function. But the hyperlink has been invalidated.

2. I downloaded the Easycap electrode location file from the availableofficial webpage, 

http://www.easycap.de/easycap/e/downloads/electrode_sites_coordinates.htm#2,

and tried to import it by "Edit-->channel locations-->Read locations". When I pressed 
the "Read locations" and selected the location file, a pop-up list starting by 
"File format: autodetect...." appeared. But after I pressed the "OK" button,
an error came out with the following messages.

Undefined function or variable "eloc".

Error in readlocs (line 458)
   if isfield(eloc, 'sph_theta_besa')

Error in pop_chanedit (line 664)
                        [chans] = readlocs(tmpargs{:});
 
Error using waitfor
Error while evaluating uicontrol Callback

3. I also tried to input the XYZ-coordinates manually, but the electrode locations
are a little strange that they are not on a unit spherical surface, it's like an 
ellipsoid surface. I am really confused, because I saw all the coordinates from your
standard .loc file have the same radius (on a unit sphere). 
What should I do when construct a 2D heap map from such kind of 3D coordinates? 

4. I am also wondering what algorithm you applied when topoplot. Something about 
Current Source Density and Surface Laplacian can be found over the internet,
but write such codes seems not so easy, could you give me some hints or advice
of how draw a 2D head map?

Thank you!

Best regards,
 
Guangyi Ai
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KYUSHU INSTITUTE OF TECHNOLOGY
Graduate School of Life Science and Systems Engineering
Dept. of Brain Science and Engineering
Guangyi Ai

Email: ai-kouitsu at edu.brain.kyutech.ac.jp
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