Hi Lars,
yes, the size of the faces is initially fixed - we cover the surface of each segmented wm voxel that borders non wm with 2 triangles. This gets changed by both the topology correction and the surface deformation. Note that the fsaverage surface area is less than any individual subject due to smoothing of the surface, which is why we include a correction factor in the fsaverage surfaces.
cheers, Bruce
On Wed, 16 Sep 2009, Lars M. Rimol wrote:
Hi,
I have a few questions about the surface processing stream:
I compared ?h.orig.nofix, ?h.orig, ?h.sphere and ?h.sphere.reg files. The number of triangles and vertices changes between the first two but after that they're constant. But the numbers are different across subjects. For fsaverage the number of vertices is consistently 163 842 and the number of faces 327 680.
Therefore, I assume that during the tesselation step in the processing stream, different subjects get different numbers of vertices due to differences in brain size. (And that the fsaverage numbers reflect average brain size.) Is that correct?
And does this mean that the size of the faces/triangles is uniform across all locations and subjects, at least before the topology fix?
Thank you!
Lars M. Rimol