[FieldTrip] online head position monitoring not working

[Andreas Wollbrink]

Dear Fieldtrip community,

while trying to integrate online head-position monitoring into our standard pipeline during MEG recordings with our CTF WC 275 channel system, 
I noticed that the ‘ft_realtime_headlocalizer’ function (as in the attached example script aw_trackHeadPosition) applied on Matlab (e.g. applied on
our stimulation computer) terminates with the following message:

Error Message:

Unrecognized field name "grad".

Error in ft_realtime_headlocalizer (line 115)
isneuromag = ft_senstype(hdr.grad, 'neuromag');
^^^^^^^^
Error in aw_trackHeadPosition (line 7)
ft_realtime_headlocalizer(cfg);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The problems seems to happen only when I transfer (live) data using the Linux command-line program ‘ctf2ft_v3’ or when I transfer an existing dataset
using the 'ft_realtime_fileproxy' function 
(see the scripts in the appendix for an example) both from the acquisition computer.

When I play back the head movements from the same dataset using the `ft_realtime_headlocalizer` function (see attached script aw_replayHeadPosition.m)
on the same computer as above (e.g. stimulation computer), everything works.
So the `grad` structure is essentially present in the data set (header).

Has anyone else had a similar experience, or perhaps even found a solution?

Please let me know if you need any additional information.
 
Thanks a lot for the help.

Best, Andreas




-- 
Andreas Wollbrink, Dipl.-Ing., Biomedical Engineer

Lab Manager
IT-Administrator

University Hospital, University of Muenster
Institute for Biomagnetism and Biosignalanalysis

Malmedyweg 15, 48149 Muenster, Germany

office:    +49-251-83-52546
email: a.wollbrink at uni-muenster.de
web: https://www.medizin.uni-muenster.de/biomag/das-institut/mitarbeiter/andreas-wollbrink.html

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Unrecognized field name "grad".

Error in ft_realtime_headlocalizer (line 115)
isneuromag = ft_senstype(hdr.grad, 'neuromag');
                         ^^^^^^^^
Error in aw_trackHeadPosition (line 7)
ft_realtime_headlocalizer(cfg);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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