Hi Katherine,
The units of distance depend on the units of the surface's node coordinates, typically that is in mm but you never know.
You have to use the .1D format, I am surprised the .niml format worked here.
Use your .1D.dset file and use the [] index selector to choose the column that has the node indices in it.
If your indices are in the first column, then use:
FILE.1D.dset'[0]'
If the indices are in the 5th column, use:
FILE.1D.dset'[4]'
cheers.
Godot