[Eeglablist] position of electrodes

[Tim Mullen]

Hi Iman,

topoplot() does not return the transformed electrode locations by default
(it should, so we'll change that), but fortunately a very small
modification to the function output will get what you want. Just edit
topoplot.m and add variables 'x' and 'y' to the list of function outputs.

i.e. replace line 193 of topoplot.m with this line:

function [*x*,*y*,handle,Zi,grid,Xi,Yi] =
topoplot(Values,loc_file,varargin)

now call topoplot as follows:

>> [x,y] = topoplot([],EEG.chanlocs,'electrodes','on');

(note you can also use {'electrodes', 'labelpoint'} or other display
options).

x and y now contain the x,y cartesian coordinates sorted in ascending order
of channel number i.e. [ x(i) , y(i) ] are the x,y coordinates for the ith
channel. The z-coordinate is the same for all channels and is hard-coded in
topoplot.m to be *z=2.1*.

Try this scriptlet to test it out:


% ---------------------------------------------

% call topoplot and retrieve x,y,z electrode locations ...

figure;

[x,y] = topoplot([],EEG.chanlocs,'electrodes','labelpoint');

z = ones(size(x))*2.1;

% ... verify the locations by drawing markers at the retrieved coordinates

%    (red markers should be exactly superimposed on original channel
markers)

hold on; plot3(y,x,z,'.r');

% ---------------------------------------------


Best,

Tim


On Tue, Dec 4, 2012 at 4:34 PM, Iman M.Rezazadeh <irezazadeh at ucdavis.edu>wrote:

> Dear EEGlabers.****
>
> Do you have any idea how can I retrieve the  position of the electrodes on
> the displayed screen after using topoplot(). The point is when using
> topoplot() it needs the electrodes location and it has its own mapping to
> display it on the screen. Now, if sb wants to use the output of topoplot()
> as layout then the location of the electrodes on the screen is important!*
> ***
>
> ** **
>
> ** **
>
> Iman M.Rezazadeh, PhD****
>
> Postdoctoral Research Fellow****
>
> Center for Mind and Brain****
>
> University of California, Davis****
>
> irezazadeh at ucdavis.edu****
>
> Cell:310-490-1808****
>
> Skype: Imanmr****
>
> ** **
>
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