Hello,
I have FreeSurfer surface models created from Talairached AFNI (+tlrc) briks. I am interested in computing distances between nodes on these (orig or smoothwm) surfaces in mm units. The +tlrc briks are 161mm (R-L) X 191mm (A-P) X 151mm (I-S). with 1X1X1 mm^3 voxels. talairach.xfm or any such files or transformations were not used. As I understand, FreeSurfer would resample this brik into a 256 X 256 X 256 RAS coordinate space. There are the coordinates you see when you look at say a ?h.smoothwm.asc file. To interpret these coordinates in terms of mm, one could multiply the X coordinate by 161/256, Y by 191/25, and Z by 151/256. The distance between two nodes computed with these modified coordinates should be in mm. Is this correct or am I missing something?
thanks, Rutvik