evoked : Evoked | Epochs | Raw 
The measurement file. Need to have info attribute. 
 
trans : str | ‘auto’ | None 
The full path to the *-trans.fif file produced during
coregistration. If present or found using ‘auto’
the maps will be in MRI coordinates.
If None, map for EEG data will not be available. 
 
subject : str | None 
The subject name corresponding to FreeSurfer environment
variable SUBJECT. If None, map for EEG data will not be available. 
 
subjects_dir : str 
The path to the freesurfer subjects reconstructions.
It corresponds to Freesurfer environment variable SUBJECTS_DIR. 
 
ch_type : None | ‘eeg’ | ‘meg’ 
If None, a map for each available channel type will be returned.
Else only the specified type will be used. 
 
mode : str 
Either ‘accurate’ or ‘fast’, determines the quality of the
Legendre polynomial expansion used. ‘fast’ should be sufficient
for most applications. 
 
meg_surf : str 
Should be 'helmet' or 'head' to specify in which surface
to compute the MEG field map. The default value is 'helmet' 
 
origin : array-like, shape (3,) | str 
Origin of internal and external multipolar moment space in head
coords and in meters. The default is 'auto', which means
a head-digitization-based origin fit. 
 
n_jobs : int 
The number of jobs to run in parallel. 
 
verbose : bool, str, int, or None 
 
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