1) Those files was export of Curves (not 2-vertex polylines) but with polylines OBJ looks same.
2) Single line without polygon is a polyline. Polyline with two vertices is exported as pure vertices without edges.
3) I`ve thought about vertex ID but if you will edit a curve then a vertex order will be broken so it`s not a solution

I wanted to do in that way becouse I do retopo on the surface of big 3d scan data. I`ve thought that I could do curve retopo in Modo and next build patches in MoI.

Thanks Michael for that Subd feature. It`s fantastic and it`s super feature. Only for that one feature it`s worth to buy your wonderfull software.

As I wrote before I solved my way to import curves from Modo to MoI as polygon strips. Maybe it`s not 100% accurate but I think it`s good enough.

I would like to ask about second way (MoI->Modo). Why obj export can`t export MoI curve without surface as f.e. polyline? Of course I can do same trick in other way. Build surface only to cheat exporter and remove it in Modo to have polylines which can be coverted to curves.

Edit: I`m not super specific becouse I have my Modo based workflow and with that thread I`m trying to do research of potential possible changes in my current workflow.

Cheers!!!!