One of the ways you can do this, with panelling tools, is something like this:
1 - Create the grid on the surface->Panel2D from Grid (make sure to add edges)
2- ungroup the edges
3 - join edges in U Direction->Group
4- join edges in V Direction-> Group
5 - fin edges with U curves
6 - fin edges with V curves.
EDIT: I just tried this again, and you don’t need to do steps 2 - 6! You can just add the edges, then run the ptfin command! (you do need the base surface to reference, this is where it gets the surface normal direction from)
or you could recreate the PTFin command in GH, (using paneling tools for GH).
NOTE: This example uses Rhino 6 with Paneling tools plugin for Rhino and GH, (although I think the current pt installer gives you both so I don’t think you need to do a separate install)
PTGrid_ManualGHPTFIN.gh (12.5 KB)