[Mne_analysis] CSD might break montage

[Gabriel Weindel]

        External Email - Use Caution        

Hello all,

I am applying CSD to my epoched data and want to compare the 
distributions of the ERPs on the scalp before and after surface laplacian.

epochs_csd = mne.preprocessing.compute_current_source_density(epochs)

I use : mne.viz.plot_compare_evokeds([epochs.average()], picks='eeg', 
axes='topo')
To plot before CSD, everything works fine but then I use :
mne.viz.plot_compare_evokeds([epochs_csd.average()], picks='csd', 
axes='topo')
And then the channel order is preserved but the cartoon head is shrinked 
to the lower left of the figure (see attached) making it impossible to read.

I am assuming that the montage is lost in the csd transform as 
epoch.info prints me :
<Info | 11 non-empty values
  bads: []
  ch_names: Fp1, AF7, AF3, F1, F3, F5, F7, FT7, FC5, FC3, FC1, C1, C3, 
C5, ...
  chs: 64 EEG
  custom_ref_applied: True
  dig: 712 items (3 Cardinal, 64 EEG, 645 Extra)
  file_id: 4 items (dict)
  highpass: 0.0 Hz
  lowpass: 40.0 Hz
  meas_date: 2019-06-06 11:46:59 UTC
  meas_id: 4 items (dict)
  nchan: 64
  projs: []
  sfreq: 1000.0 Hz
 >

and epochs_csd.info :

<Info | 11 non-empty values
  bads: []
  ch_names: Fp1, AF7, AF3, F1, F3, F5, F7, FT7, FC5, FC3, FC1, C1, C3, 
C5, ...
  chs: 64 CSD
  custom_ref_applied: True
  dig: 712 items (3 Cardinal, 64 EEG, 645 Extra)
  file_id: 4 items (dict)
  highpass: 0.0 Hz
  lowpass: 40.0 Hz
  meas_date: 2019-06-06 11:46:59 UTC
  meas_id: 4 items (dict)
  nchan: 64
  projs: []
  sfreq: 1000.0 Hz
 >

Is there a quick workaround ?

Best,
Gabriel
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