> Now, what happens if I merge the vertices in another program. Will it
> create some mess in the UV coordinates ?

Yeah, they'll likely be a bit blurry right along that seam. Imagine that you're wrapping a bitmap around a cylinder for instance. For the bitmap to come out crisp along the seam edge, there can't just be one UV coordinate there, one side needs to have a UV for the start of the bitmap, and poly from the other side needs to have a UV for the end of the bitmap, even though they are ending on the same location along the seam. It's possible that some software might be able to handle it better if they keep track of UV coordinates per polygon face instead of per polygon vertex though. Hmm, come to think of it .obj actually allows one to specify different uvs per-face like this (distinct from the xyz vertex location) so I suppose I can support it... I'm not exactly sure how well supported this is by most .obj importers though.

- Michael