The coordinates

[Robert Oostenveld]

Hi Feng,

Fieldtrip does not have it's own coordinate system but uses the
coordinate system that is implicit in the data: the gradiometer
positions and head model are (usually) obtained from the data files
generated using the software of the MEG system. For CTF, the
coordinates are expressed in cm, except for anatomical MRIs, which
are expressed in mm. The various coordinate systems (including the
description of how the axes are linked to the head) are explained in
more detail on

http://www2.ru.nl/fcdonders/fieldtrip/doku.php?
id=fieldtrip:documentation:frequently_asked_questions#how_are_the_differ
ent_head_and_mri_coordinate_systems_defined

best
Robert

On 9 May 2006, at 1:24, Rong, Feng (NIH/NIDCD) [V] wrote:

> Hi,
> I have a question about the grid coordinates calculated with
> prepare-leadfield.m -- how to interpret the .pos value?
> For example, I run the script [grid]=prepare_leadfield(cfg,freq),
> with the xgrid, ygrid, and zgrid value of cfg being set as 'auto',
> then how can I interpret the grid.pos value? They have the value
> like [-9 2 2], which coordinates is it?
>
> Best,
> Feng Rong
> Graduate Student
> NACS Program / Kinesiology Dept
> UMCP
>