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