I created a scalp surface mesh with mkheadsurf. I need to mark or select some scalp surface points and obtain their MRI coordinates. That is, if my MRI is 256-cubed I need the (ix,iy,iz) MRI voxel coordinates closest to the scalp mesh point I mark, where these run from 1 to 256 (or 0-255 if you must).  The tksurfer display shows several types of floating point coordinates, but they assume an origin in the center of the head somewhere. If I knew the MRI coordinates of this origin I could calculate the original MRI.

Thanks,

-Jeff