[FieldTrip] 96 channel ActiCap sensor locations

Andrew Chang changa5 at mcmaster.ca
Sat Feb 25 21:38:34 CET 2017


Thank you, Julian! Your comments are very helpful. It's working well!

For the future reference of other Fieldtrip users, here are my codes of
implementing it.

sphcoor = [Theta,Phi]'; % combining theta and phi coordinates
cartcoor = elp2coor(sphcoor)'; % converting theta/phi coorfinates into xyz

data.elec.elecpos = cartcoor;
data.elec.chanpos = cartcoor;
data.elec.label = ChannelName; % 'ChannelName' is a cell array of channel
labels
data.elec.unit = 'm';
%
plot3(data.elec.elecpos(:,1),data.elec.elecpos(:,2),data.elec.elecpos(:,3),'r*')
% just check the positions

% make a fieldtrip layout file
cfg = [];
layout = ft_prepare_layout(cfg,data);
cfg.layout    = layout;
ft_layoutplot(cfg,layout); % check the layout


Here is the function converting the theta/phi coordinates to
xyz-coordinates you can use in FieldTrip (Written by Stephan Moratti @UCM).

% Convert electrode positions in polar coordinates (theta, phi like from
*.elp-files)
% into cartesion coordinates
% Electrode positions are assumed to lie on a sphere with radius "radius"
(=1 if not specified)
% sphcoor(2, number of sensors), cartcoor(3, number of sensors)
% Written by Stephan Moratti moratti at med.ucm.es

function cartcoor = elp2coor(sphcoor, radius);

factor = pi/180;

if nargin == 1
radius = 1.0;
end;

[m n] = size(sphcoor);

for i=1:n
projxy = sin(factor*sphcoor(1,i));
cartcoor(3,i) = cos(factor*sphcoor(1,i));

cartcoor(1,i) = projxy*cos(factor*sphcoor(2,i));
cartcoor(2,i) = projxy*sin(factor*sphcoor(2,i));
end;

cartcoor = radius*cartcoor;


Best,
Andrew

On Sat, Feb 25, 2017 at 2:31 PM, Julian Keil <julian.keil at gmail.com> wrote:

> Hi Andrew,
>
> I attached you a function to convert the theta/phi coordinates to
> xyz-coordinates you can use in FieldTrip (Written by Stephan Moratti @UCM).
> To actually use the result, you need to build an electrode structure, so
> do something like this:
>
> cap=importdata('128_channel_easycap.elp'); % Import the Vendor-Provided 3d
> Positions
>
> %% Step 2.1. Make an electrode file
>
> elec.pnt=elp2coor(cap.data',100)';
> elec.label=cap.textdata;
>
> %% Check the positiosn on the head surface. They don't look good, do they?
>
>  figure
>   triplot(vol.bnd(1).pnt, vol.bnd(1).tri,  [], 'edges');
>  hold
>  plot3(elec.pnt(:,1),elec.pnt(:,2),elec.pnt(:,3),'r*')
>
>
> %% Step 3 Move the electrodes to match the head
>
>   cfg=[];
>   cfg.method='interactive';
>   cfg.elec=elec;
>   cfg.headshape=vol.bnd(1);
>
>
>   elec_new=ft_electroderealign(cfg);
>
>
> Good luck,
>
> Julian
>
>
>
>
> ********************
> *Dr. Julian Keil*
>
> AG Multisensorische Integration
> Klinik für Psychiatrie und Psychotherapie
> der Charité im St. Hedwig-Krankenhaus
> Große Hamburger Straße 5-11, Haus 2
> 10115 Berlin
>
> Telefon: +49-30-2311-1879 <+49%2030%2023111879>
> Fax:        +49-30-2311-2209 <+49%2030%2023112209>
> www.multisensorymind.com
>
>
>
> Am 25.02.2017 um 16:39 schrieb Andrew Chang:
>
> Dear FieldTrip users,
>
> I am wondering whether anyone would like to share the Fieldtrip layout
> file of the "*actiCap 96Ch Standard 2*" EEG cap with me. I have checked
> around the websites of Fieldtrip and Easycap, but failed to find anything
> useful. So far I only got it's top-view map and it's Theta/Phi Coordinates
> (see the attached PDFs in the links below).
> https://www.dropbox.com/s/wlshxqb93tn4duz/actiCAP-96-
> channel-Standard-2.pdf?dl=0
> https://www.dropbox.com/s/6bva7az6ydc6hvh/actiCap-96Ch-
> Standard%202%20Theta_Phi_CAP.pdf?dl=0
>
> It would be very appreciated if anyone can share the Fieldtrip layout file
> with me, or teach me how to create a layout in Fieldtrip from Theta/Phi
> Coordinates.
> Thank you all in advance!
>
> Sincerely,
> Andrew
>
>
> --
> Andrew Chang, Ph.D. Candidate
> Vanier Canada Graduate Scholar
> http://changa5.wordpress.com/
>
> Auditory Development Lab
> Department of Psychology, Neuroscience & Behaviour
> McMaster University
> _______________________________________________
> fieldtrip mailing list
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>
>
>
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> fieldtrip mailing list
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>



-- 
Andrew Chang, Ph.D. Candidate
Vanier Canada Graduate Scholar
http://changa5.wordpress.com/

Auditory Development Lab
Department of Psychology, Neuroscience & Behaviour
McMaster University
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