I'm not sure what you are trying to do here. Ico7 is just a 7th order icosahedron and does not "belong" to any subject. What belongs to fsaverage or fsaverage_sym is the atlas of curvatures and registrations derived from them (eg, lh.sphere.reg). It might be easier to use mris_apply_reg rather than mri_surf2surf. One of the reasons I wrote mris_apply_reg was to apply the xhemi registrations because the structure of mri_surf2surf makes it really hard to get the specification right.

On 2/15/19 7:41 PM, Alon Baram wrote:

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Hello,

I am trying to understand some code I came across and am having trouble understanding the difference between the target surface in mri_surf2surf and the surface used as target for the registration. The code first uses freesurfer_registerXhem register the subject's right hemisphere to the left and register both hemispheres to fsaverage_sym, producing the registration file fsaverage_sym.sphere.reg.

I then use the following command:

mri_surf2surf --srcsubject $subj  --hemi lh --trgsubject ico--trgicoorder 7 --surfreg fsaverage_sym.sphere.reg --srcsurfval temp.curv --src_type curv --trgsurfval tempN.curv --trg_type curv --mapmethod nnf --nsmooth-out 1

to resample the registered subject surface to ico7. To my understanding, ico7 is exactly the same as fsaverage, but fsaverage is not exactly the same as fsaverage_sym. So I find it strange that the code is using a registration file which is registered to one surface (fsaverage_sym) with a different target surface (fsaverage).

I'm not sure which space the result will actually be in - fsaverage or fsaverage_sym?

I'm obviously missing something basic here.

Thanks very much for the help!

Alon

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