[Eeglablist] position of electrodes

[Tim Mullen]

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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>>
>>
>>
>> --
>> ---------  αντίληψη -----------
>>
>
>
>
> --
> ---------  αντίληψη -----------
>



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