I have seen at least three ways for identifying an intermediate surface between the white and pial surfaces:

- Multiply the surface normal vector for each white surface vertex by half of the cortical thickness and add it to each vertex coordinate

- Average the white and pial coordinates for each vertex

- Use mris_expand, e.g. `mris_expand -thickness lh.smoothwm 0.5 lh.graymid`

I have found that these approaches all give similar, but not identical results.

Is there a consensus that one approach is best relative to the others?

Thanks,

Michael