Import 3D scanner digitized electrode locations into BST

[Raymundo.Cassani]

Hi Nicola,

Registration between the CTF helmet (and the coils) and the Subject is done by having two pairs of fiducials: (i) fiducials in the subject anatomy, (ii) fiducials in the sensors coordinates (helmet). With the process that you describe, in FieldTrip the first set are the fiducials that are acquired by finding them in the head surface. And the second set are the fiducials for the CTF coordinates. With all this said

@nscheinhaut

As far as I understand, BST also uses the CTF coordinate system, and BST definition looks identical to Fieldtrip one.

Yes, Brainstorm uses the Subject Coordinate System (SCS), which is defined as the CTF system.
https://neuroimage.usc.edu/brainstorm/CoordinateSystems

@nscheinhaut

Following this logic, I directly imported the electrode locations computed from Fieldtrip into BST via import channel file > EEG: ASCII: Name,XYZ (,). Since the fiducials are integrated into the ctf coordinate system, as far as I understand there is no need to also import the fiducials in BST.

In Brainstorm, the SCS is generated from the position of the fiducials on the subjects anatomy (this is the set (i) from the first paragraph above). As such, the coordinates exported from FieldTrip in the way described above, will be correct if-and-only-if the position of the first set of fiducials (i) are the same in Brainstorm and FieldTrip.