[FieldTrip] Bug in ft_megplanar? (Version 20121209)

George Wallis wallisgj at gmail.com
Mon Dec 17 17:37:09 CET 2012


The electa machine has 2 physical planar gradiometers at each sensor 
location, which are oriented orthogonally to one another (it also has a 
magnetometer at each sensor location).  I believe ft_megplanar 
synthesises planar gradiometer data from, for example, data collected 
using axial gradiometers (I'm not sure - we've got an electa scanner, 
so  I haven't used it!).  But essentially, it's creating virtual sensors 
of a type the neuromag scanner already has in the hardware.

Instead, you might want to take the two planar gradiometer sets, and 
combine them, so that for each sensor location you have a single 
gradiometer value (you'll still have the magnetometer data in 
addition).  ft_combineplanar does this: it takes the signal from each 
gradiometer at each sensor location, and combines them into a single 
scalar signal.  You can tweak the method it uses to do this, but in the 
time domain I think it just finds the cartesian sum (sqrt( s1^2 + s2^2) 
where s1 and s2 are the signals from each sensor).

best wishes,

On 17/12/2012 16:22, clme at tf.uni-kiel.de wrote:
> Hello ft-users,
> Today I tried to plot planar gradients for neuromag306 data.
> When calling avgFICplanar        = ft_megplanar(cfg, avgFIC);
> I get the following error:
> ??? Error using ==> ft_checkdata at 406
> This function requires ctf151, ctf275, bti148, bti248, itab153,
> yokogawa160 or yokogawa64 data as input, but you are giving
> neuromag306 data.
> Error in ==> ft_megplanar at 106
> data = ft_checkdata(data, 'datatype', {'raw' 'freq'}, 'feedback', 'yes',
> 'hassampleinfo', 'yes', 'ismeg', 'yes',
> 'senstype', {'ctf151', 'ctf275', 'bti148', 'bti248', 'itab153',
> 'yokogawa160', 'yokoga
> Error in ==> reading_fif_planar at 39
> avgFCplanar        = ft_megplanar(cfg, avgFC);
> When manually adding ",'neuromag306'" to the senstype in line 106 and
> commenting out line 297 erverything seems to work as it should.
> Is this a bug or am I doing something wrong?
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