Hi Jorge,
yes, the area of a vertex is 1/3 of the area of all triangles that it is a member of, and it should sum to the area of the surface. The average subject has a correction factor that accounts for the "lost" area due to averaging, so you'll need to apply this if you want it to be in true mm (in the average sense across your subjects). mris_info ~/local_subjects/fsaverage/surf/lh.white reading group avg surface area 864 cm^2 from file Reading in average area /homes/4/fischl/local_subjects/fsaverage/surf/lh.white.avg.area.mgh SURFACE INFO ======================================== type : MRIS_TRIANGULAR_SURFACE=MRIS_ICO_SURFACE num vertices: 163842 num faces : 327680 num strips : 0 surface area: 70394.8 AvgVtxArea 0.429650 AvgVtxDist 0.757401 StdVtxDist 0.227951 group avg surface area: 86444.7 . . .
thus, you would need to multiply your areas by 86444.7/70394.8 to get mm in the average cross-subject sense. cheers, Bruce
On Sun, 29 Jun 2008, jorge luis wrote:
Hello all I have some questions:
I would like to know how freesurfer computes the vertexÿÿs wise areas? eg. thouse in lh.area.
It should be expected that the sum of the areas of all the vertices across a surface equals the total surface area?
To be much specific: Can I compute the area of an 'activated' cortical ROI in the average
subject by simply adding the area of all its vertices?
In adavance thank you
Jorge Phd Student
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