reading bdf+ files?

[Robert Oostenveld]

Hi Thomas,


On 8 Mar 2010, at 10:30, Thomas Hartmann wrote:
> thanks for the quick answere.
> yes, bdf+ is bdf with an annotation-channel added. this channel is unlike the bdf trigger channel. so this, as i had already expected, explains the problem.
> 
> my major motivation for using bdf+ is the availability of a ready-to-use c++ library. unfortunatly it only writes bdf+ or edf+, not the "standard" format.
> 
> does someone know of a stable, well-documented, free library (c or c++) to write eeg-data in a format, fieldtrip can read?


I would probably write it in a brainvision analyzer alike format. Although I am not aware of formal/official documentation, the file format is very simple (and widely supported). It consists of an ascii header file (*.vhdr), an ascii marker file (*.vmrk) and a binary file with the data. Although the data file is normally binary, it can also be ascii (but that makes reading it very inefficient).

The ascii header file (ini-like) explains the format of the binary file, which can have different data formats (int16,32 and probably floats) and be multiplexed or not. 

On ftp://ftp.fcdonders.nl/pub/fieldtrip/tutorial/subj2.zip you can find some example data which is used in http://fieldtrip.fcdonders.nl/tutorial/continuous. I don't know the details of that particular dataset, but probably it is pretty standard. I guess it has 64 channels 32 bit continuous recording with 5 to 10 different trigger values in it. Combined with fieldtrip/fileio/private/read_brainvision_vhdr, read_brainvision_eeg and read_brainvision_vmrk you can probably easily figure out what the file format is. Writing the two text files and a binary multiplexed file could easily be done without a C++ library. I just realised that in fieldtrip you can also export to that file format using the write_data function. Have a look in fieldtrip/fileio/private/write_brainvision_eeg for the details of the simplest format. 

Hmm, a more challenging problem from the C++ perspective then is to implement the accompanying *reader* for it. In Matlab that is simple, but parsing the text files in C++ and going over all possible options and sub-formats would be non-trivial in C++. You might want to have a look at http://biosig.sourceforge.net/projects.html to see whether that provides a C++ solution.

best regards,
Robert

 

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