[FieldTrip] 642 nodes for source model based on cortical sheet
Tom Holroyd (NIH/NIMH) [E]
tomh at kurage.nimh.nih.gov
Wed Dec 5 17:27:39 CET 2012
I think the model in question consists of one dipole at each vertex of a recursive subdivision of some platonic solid, such as a triangular subdivision of an octahedron's faces, a very popular method for generating spherical meshes. Each of these will produce a characteristic number, and in particular for a triangulated icosahedron it's 2 + 10 * 2**(d*2), where d is the recursion depth, which for d = 3 turns out to be 642. So your "cortical sheet" is probably a triangulated icosahedron with spherical topology. It may not look like a sphere. The mesh is allowed to deform. Somewhere in the code you could maybe make a new spheremesh, for the next d of 4, you get 2562 nodes. If you want more.
andrea brovelli wrote:
> Dear all,
> I am constructing a source model based on cortical sheet and I get
> always 642 nodes.
> I tried to track down this magic number and I have found that at lines
> 209 and 229 of ft_prepare_sourcemodel.m you fix it to:
> cfg.spheremesh = ft_getopt(cfg, 'spheremesh', 642); % FIXME move
> spheremesh to cfg.grid
> What was the rationale behind this ?
> Did you modify this in more recent versions of Fieldtrip or how could we
> have it in the cfg in the future ?
> Thanks a lot
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> fieldtrip at donders.ru.nl
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