Hi Mike,

Perhaps your volume data is not overlaying the Surface Volume
dataset (because either it is only a partial volume, or because
they are not aligned). In such a case, 3dVol2Surf does not give
results for those nodes that do not overlap any voxels.

If that is the case, but you want to proceed, consider the
-oob_value option in 3dVol2Surf, to include output for those
nodes that are "out of bounds" (outside the boundaries of your
'-grid_parent' dataset).

On a similar note, there is an '-oom_value' option for the case
where you apply a mask, but want output for all of the nodes.

See '3dVol2Surf -help' for more details.

- rick