[FieldTrip] why does ft_denoise_synthetic inserts NaNs in grad fields

[Alexander Backus]

Hi,

When I use ft_denoise_synthetic on my preprocessed CTF275 MEG data to
covert to 3rd order gradient, it replaces the values in data.grad.chanpos
and data.grad.chanori with NaNs.

I assume this is done because they are no longer valid.
When digging into the low-level code I found something about mismatching
number of channels.

Anyway, when I want to subsequently covert to planar gradient (does this
actually makes sense?) or create a source model, I need these grad values.

I have two questions:

1) What does ft_denoise_synthetic exactly do (in non-math terms) and why
are NaNs inserted in the grad subfields?

2) Can I still use the data for planar gradient conversion or source
modeling by using the earlier stored old gradient info (pre
ft_denoise_synthetic) or is this ill-advised and is there a more wise
course of action?

Thanks in advance,
Best,
Alexander Backus


-- 
Alexander R. Backus, MSc
PhD Candidate at the Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Memory and Space Research Group
www.doellerlab.com

P.O. Box 9101, NL-6500 HB Nijmegen , The Netherlands
Telephone: +31(0)24 36 10754
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