OBJ with Vertex Group export and import I have a problem while exporting and importing vertex groups data through OBJ format. I have certain vertex groups in my object which consist of only single vertex (as shown in the following two images)

Now I export it by checking the 'polygroups' option and the 'keep vertex order'option in the OBJ export options and then import it by checking the 'Polygroups' option under 'Keep Vertex Order' tab in the OBJ import options. I see that, as expected, the vertex order is maintained, but when I tried selecting the vertex groups, I am selecting faces (as shown in the following images). How can I prevent this from happening? Why is the vertex group with single vertex changing into a vertex group with 4 vertices and the corresponding face is getting selected when the vertex group is selected?
Ok, I've just been testing myself, basically it's what I said before. OBJ file format specification probably doesn't support "vertex groups" feature.
There is no such structure or way to store that information in this file format.

What blender does apparently try to map vertex groups to the "poly groups" feature of OBJ. Since polygroups - as the name implies - only stores groups of faces it as a few caveats as it can't unequivocally map vertex groups to faces, so it can't store certain cases like single isolated vertex from vertex groups.

The minimum supported is probably three vertex, which is the least possible to define a face. This is what my four-corner vertex group (to the left) was imported like, two separate meshed with the four corners separated from the main one (colors for clarity purposes).



So short answer is it is not supported, either find another file format that supports this, recreate you vertex groups in your destination application, or fix them by hand there.