[Eeglablist] position of electrodes

[Arnaud Delorme]

I agree with Tim that the best way to output electrode position on the screen is to return the electrode coordinates after transformation.

Arno

On 4 Dec 2012, at 20:18, Tim Mullen wrote:

> PPPS(!): note also that, for various reasons, the roles of the variables named 'x' and 'y' are interchanged inside topoplot.m -- so the internal variable 'x' actually refers to the ordinate (y-axis) and 'y' refers to the abscissa (x-axis). That's why I wrote plot3(y,x,...) instead of plot3(x,y,...). Naturally this is confusing, so in the near future topoplot will be modified to output x,y,z electrode locations with the expected interpretation.
> 
> Tim
> 
> 
> On Tue, Dec 4, 2012 at 8:00 PM, Tim Mullen <mullen.tim at gmail.com> wrote:
> PPS: the following option (which uses "~" denote missing outputs, avoiding the need to save a separate function) was pointed out by a user. I didn't suggest this because the "~" notation was only introduced in Matlab 2009b. But if you have 2009b or later, it's a good option.
> 
> ---------- Forwarded message ----------
> From: Tide Gu <tidegu at me.com>
> 
> Why not put x, y at the end of parameters? i.e., 
> 
> function [handle,Zi,grid,Xi,Yi, x,y] = topoplot(Values,loc_file,varargin) 
> 
> I think if you do so, it won't conflict with other EEGLAB functions and you can call:
> 
> >> [~,~, ~, ~, ~, x,y] = topoplot([],EEG.chanlocs,'electrodes','on');
> 
> to access x and y.
> 
> Although it kind of complex and weird, but you don't need to save a new file :)
> 
> Regards,
> 
> Tide
> 
> -----------------------------------------------
> Tide / Shenkai GU
> 
> Department of Computing, FEPS
> University of Surrey
> Guildford, Surrey
> GU2 7XH, United Kingdom
> -----------------------------------------------
> 
> 
> Tim
> 
> 
> On Tue, Dec 4, 2012 at 7:29 PM, Tim Mullen <mullen.tim at gmail.com> wrote:
> PS: for now, you should probably save the modified topoplot.m as a separate function (i.e. topoplot2.m) since other EEGLAB functions that call topoplot may throw errors if they expect the output sequence to be in its original form. Note that it doesn't fix the problem to move the new (x,y) outputs to the end of the output sequence, since most of the preceding outputs are not defined when the first argument to topoplot() is empty and this will also throw an error.
> 
> Tim
> 
> 
> On Tue, Dec 4, 2012 at 7:21 PM, Tim Mullen <mullen.tim at gmail.com> wrote:
> 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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