Missing 'elec' field when reading neuroscan CNT files?

[Durk Talsma]

Hi Folks,

I just ran into the following issue. For an ongoing EEG project, which
was originally stored in neuroscan CNT files, I'm trying to set up a
clusterrandanalysis. The analysis doesn't run, because the input data
struct is expected  to have an 'elec' field (in order to compute the
neighbouring channels).

Just looking at some CTF MEG data, I saw that these data structs do
contain the (for these puposes) equivalent 'grad' field, consisting of
the following data members:

grad.pnt
grad.ori
grad.tra
grad.label
grad.units

I suspect that elec will be similar, but which fields are required? I
suspect pnt, tra, label, and unit. Assuming this is correct, I have the
following questions:

In what coordinate system is elec.pnt specified? (Cartesian, polar?
Which reference frame?)
What is the meaning of the tra field?

Cheers,
Durk