[Freesurfer] generating new surface

Dear Freesurfers,

I need to generate a surface which lies halfway between the wm/gm border and the pial surface so that I can then import it in matlab using read_surf.m to get the vertex coordinates and faces for the surface that, as I said, would not be the pial surface, but defined at half cortical thickness.

I looked at mri_vol2surf --help, and its option --projfrac 0.5 seemed to be what I wanted, but I don't know how to call mri_vol2surf for the specific needs I have.

Also, mri_vol2surf produces an overlay mappable onto a surface and not a surface per se, so maybe what I am looking for lies elsewhere.

Any help would be highly appreciated!!

ian