[Mne_analysis] MNE Matlab fiff_write_coord_trans function help

[Kambiz Tavabi]

Hi Dan,

Thanks for pointing me mne_ex_read_write_raw. It seems to work for the 
most part, i.e., writing a new raw file minus the MISC channels. There 
is the option to change the data at Line 98 "add your own miracle here". 
But alas a miracle I cannot conjure. In all my attempts I cannot manage 
to change the desired recording information (info.dev_head_t), this 
information is always copied from the original input file argument. So 
I'm forced to ask, have you actually managed to change the recording 
information using mne_ex_read_write_raw? or is that even possible?

Kambiz


On 10/25/2012 6:39 AM, dgw wrote:
> Hi Kambiz,
>
>  From your description of approach "a" it seems like you should start a
> bit closer to the beginning. i.e. read the raw fiff file change the
> device to head transformation matrix and write it out again. You
> shouldn't need to deal with those other functions. I would use
> mne_ex_read_write_raw as a guide. I am not sure of what you tried to
> do exactly, but the above approach is simpler. It sounds as though you
> were trying to simply overwrite directly into an already written file,
> which I do not believe is supported in the MATLAB toolbox (or if it
> is, it may be more complicated to use than simply reading in the file
> and writing it out again). You need to read in the whole file and
> write it back out.
>
> D
>
> On Wed, Oct 24, 2012 at 6:38 PM, Kambiz Tavabi <ktavabi at uw.edu> wrote:
>> Greetings all,
>> I accidently sent this email to mne_support at nmr, if you're getting this
>> again, I am sorry for the duplicate.
>> I am trying to define a new device-to-head transformation matrix and either
>> (a) over write the transformation matrix in a existing raw fif file or (b)
>> write a new 'dummy' fif file. I get the impression option (a) is more
>> feasible, using some of the MNE Matlab functions.
>> To that end I tried using the function fiff_write_coord_trans to overwrite a
>> coordinate transfomation structure to a raw fif file. The device-to-head
>> transformation matrix output from fiff_read_meas_info is of type double
>> precision, once I make the desired changes to that matrix and pass the new
>> coordinate transfomation structure to fiff_write_coord I get an error at
>> line 53:
>>
>> ln51-count = fwrite(fid,int32(FIFF_COORD_TRANS),'int32');
>> ln52-if count ~= 1
>> ln53-   error(me,'write failed');
>> ln54-end
>>
>> I suspect the problem is due to mismatch between 'int32' and 'double'
>> precision types. But I get the same error if I convert the transformation
>> matrix to int32, not to mention the values are now quite different as
>> compared to the original double precision matrix output by
>> fiff_read_meas_info.  Anyone know what's going on here? or know of a fix or
>> workaround?
>>
>> Thanks in advance
>> Kambiz
>>
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-- 
--------------------------------------------------
Kambiz Tavabi PhD
Institute for Learning & Brain Sciences
1715 Columbia Road N
Portage Bay Building
Box 357988
University of Washington
Seattle, WA 98195-7988
Tel: 206-221-6415
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