Problem with BESA coordinate system

Robert Oostenveld r.oostenveld at FCDONDERS.RU.NL
Sun Mar 11 15:12:13 CET 2007

Dear Chen

On 9 Mar 2007, at 15:11, Y Chen wrote:
> I used "besa2fieldtrip.m" and "read_fcdc_elec.m" to load BESA .avr
> file
> and .sfp electrode file, then used "topoplotEP.m" and got the attached
> plot. Looks like the coordinate is wrong (90 degree shift). Form your
> website introduction, the BESA coordinate is right. However in the
> software implementation, would you please double check it? I could
> send in
> my files if you want. Thanks.

The read_fcdc_elec does not know about the coordinate system, and
just reads the electrode locations in the way they are represented in
the file. In FieldTrip we do not have a fixed coordinate system.
However, the topoplotting functions do have a fixed layout of the
head, i.e. the schematical drawing of the head (the circle, with the
triangle as nose and with the ears) always has the nose at the top.
The nose position is at the moment not an option that you can specify
in topoplot (it might make sense to implement a
cfg.noseposition='positiveY' or 'positiveY'). That means that for
topoplottting at the moment you have to rotate your electrode
positions (elec.pnt) by 90 degrees.

best regards,

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