Generating intermediate surfaces


I am a new AFNI user and am trying to carry out some surface based analysis using COSMO MVPA. Part of the pre-processing requires me to generate an intermediate surface i.e. the node wise average of the pial and white surfaces, and an inflated surface with the center of mass on the medial side of the surface.

Apparently I can create these with MapIcosahedron but I can’t work out how. At the moment I am using the command
" -spec .spec -ld 64 -dset_map lh.thickness.gii.dset -dset_map lh.curv.gii.dset -dset_map lh.sulc.gii.dset -morph lh.sphere.reg.asc -prefix std.64.lhreg.c "

Could anyone offer some advise on generating the two extra surfaces that I need here?
Thanks in advance!