[Mne_analysis] Calculate forward model using digitization from eximia system

[Leonardo Barbosa]

Dear List,

I'm following this tutorial

http://martinos.org/mne/stable/auto_tutorials/plot_forward.html

and trying to compute the forward model using individual anatomical
information.

So far I got the skull/skin surfaces using mne watershed_bem, and now I'm
trying to use the mne.gui.coregistration the generate the -trans file.

However, the digitization information is an eximia .nbe file. I found a
thread about converting it to FIF

https://mail.nmr.mgh.harvard.edu/pipermail/mne_analysis/2013-March/001465.html

but it suggests using the mne_eximia2fif, and my eeg data is not acquired
with the eximia system, only the digitization.

The digitization consists of 3D positions for each electrodes + fiducial,
which I have imported into python as numpy.array.

Should I use mne.channels.read_dig_montage and update info['dig'] manually?

I tried

import mne.channels.read_dig_montage
digitization = read_dig_montage(elp=my_data[:, 1:], point_names=ch_names)

where my_data[:, 1:] are the coordinates of the electrodes in mm, and the
first 3 lines are ['nasion', 'lpa', 'rpa'] (ch_names has the strings with
the fiducial and electrodes names)

However I get this error:

===========================================

In [48]: read_dig_montage(elp=my_data[:, 1:], point_names=montage.ch_names)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-48-c58c337206f3> in <module>()
----> 1 read_dig_montage(hsp=None, elp=my_data[:, 1:],
point_names=montage.ch_names)

/home/leonardo/projects/mne-python/mne/channels/montage.pyc in
read_dig_montage(hsp, hpi, elp, point_names, unit, fif, transform,
dev_head_t)
    608             fids = apply_trans(neuromag_trans, [nasion, lpa, rpa])
    609             elp = apply_trans(neuromag_trans, elp)
--> 610             hsp = apply_trans(neuromag_trans, hsp)
    611         else:
    612             fids = [None] * 3

/home/leonardo/projects/mne-python/mne/transforms.pyc in apply_trans(trans,
pts, move)
    172
    173     # apply rotation & scale
--> 174     out_pts = np.dot(pts, trans[:3, :3].T)
    175     # apply translation
    176     if move is True:

TypeError: unsupported operand type(s) for *: 'NoneType' and 'float'

===========================================

Looks like hsp is mandatory, but I don't have the Polhemus information...

*Is there an easier way to create the -trans file and calculate the forward
model using individual electrodes positions from the eximia system (or
np.array with the electrodes coordinates for that matter)?*

Thank you very much in advance for any help,

Leonardo
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