mne.gui.coregistration() should accept instances in addition to filenames

[hoechenberger]

Currently, mne.gui.coregistration() expects the inst and trans parameters to be paths to files. This is inconsistent with how other bits of the API are are designed, and necessitates the creation of temporary files in certain workflows.

Instead, inst should accept Info, Epochs, Evoked, and Raw instances; and trans should accept Transform instances in addition to paths.

[agramfort]

+1

[larsoner]

inst should accept Info, Epochs, Evoked, and Raw instances; and trans should accept Transform instances in addition to paths

I guess if it's Epochs/Evoked/Raw we can try to get the filename from the instance. And if it's Info or the filename is None, we can just put None or <Raw instance> or something in the GUI in the "filename" field to make it clear we don't know the filename.

For trans we don't display the filename in the GUI anyway, so we can just do trans = _ensure_trans(..., 'head', 'mri') or whatever on it, as this function passes Transform instances (of the right to<->from, doing an inversion if necessary) and reads -trans.fif files (again doing a check+convert), so it shouldn't be too much work here, either.