[Freesurfer] Fake thickness map 2

Hello,

I was trying to create a cortical thickness map with constant values in order to perform some tests. At first I tried using mris_convert. I converted my thickness file into ascii:

mris_convert lh.thickness lh.thickess.asc

then I used matlab to change all the values in the last column to 2,0. I tried to convert the ascii file back to surface file by doing

mris_convert lh.thicness.asc lh.thickness

but I got "Segmentation fault". How can I convert may ascii file into a surface one?

After failling to acomplish this, I tried using the save_mgh and load_mgh file, nevertheless I'm not quite sure which input values are needed. Where can I put my fake values in the save_mgh file? And what is "vol"?

Thanks,

Ines