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I have just recently created a rifle in Blender and I am currently UV and Shadow mapping it. This is the Rifle here below. enter image description here

The rifle itself is split into two parts. One Part has been UV and Shadow mapped, coming out fine. But the main bulk of the rifle is having strange issues with its vertices on the UV map. The odd behavior is shown below. enter image description here

Does anyone know what the issue is? I have looked over the entirety of the mesh and haven't found any faults in it.
Blend file with UV problem.

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    $\begingroup$ What exactly is the odd behavior? The UV map not lining up with the baked AO? $\endgroup$ – gandalf3 Sep 21 '14 at 19:45
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    $\begingroup$ It is that bulk of vertices at the bottom of the UV. All of those vertices are being pulling into that area for some reason. $\endgroup$ – user2016 Sep 21 '14 at 19:46
  • $\begingroup$ Sounds like the seams need adjustment or something, but it's going to be hard to tell exactly what the cause is without the .blend.. Is it possible you could upload it? $\endgroup$ – gandalf3 Sep 21 '14 at 19:49
  • $\begingroup$ I can yes. How do I do that on here? $\endgroup$ – user2016 Sep 21 '14 at 20:04
  • $\begingroup$ Upload it to somewhere like pasteall.org/blend and put the link here. $\endgroup$ – gandalf3 Sep 21 '14 at 20:15
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There are a few spots with odd topology, which seem to be around the places where the UV map is behaving strangely.

Try pressing ⎈ Ctrl⇧ Shift⎇ AltM to select non-manifold topology. Ideally ⎈ Ctrl⇧ Shift⎇ AltM won't select anything, but in your file there are some interior faces:

enter image description here

And some zero length faces:

enter image description here

Try cleaning these places up a bit.

Aside from that, placing seam around the trigger seems to help a bit:

enter image description here enter image description here

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To start with, the tearing that you see is happening because the seams are not all marked properly using ctrl+e -> Mark Seam

The UV coordinates for the posted .blend look like they were done with UV Mapping-> Project From View which I feel is a pretty good place to start with something like this. It does still require a lot of corrections for the faces that are parallel to the view since they are all 2-dimensional. Those faces are essentially Edges so far as the UV Texture is concerned, they will have zero texture resolution.

There are a few places that need fixing from what I can see. I've circled a few parts that stand out.

enter image description here

Next, to deal with the overlapping trigger pieces you can select the faces and move them. They can also be shrunk down a bit to fit in the area nearby to help with packing.

enter image description here

The next image shows many of the faces that have to be re-projected using another method.

enter image description here

The seem which runs down the middle will help with mirroring but that may not be the best way to go here since mirroring something that thin will not only add more seems(which can show as artifacts) but the two thin bands that make of the rifle perimeter will have to be separated in the UV's in order to allow some room for padding. This extra space will use up texture resolution as well so there is not much gain here to mirroring those parts.

For the center line, I would just remove that entirely since now the geometry count should be about 20% less when exported. With all the center edges selected, you can use the keyboard shortcuts 'x' then 'g' for Delete->Edge Loops
*Note: so long as you do not do this to UV Island boundaries the UV's should be preserved and any textures that have already been baked should still be valid.

enter image description here

Now you can select all of the perimeter and use UV Mapping->Smart UV Project to quickly map them so they can be assessed quickly and also you can use UVs->Seams From Islands to quickly lock in the Islands. Sometimes it's easier to remove a few extra seams rather than to manually select them all in the 3D View for seam tagging.

enter image description here

Now seems(pun) like a good time to add a texture that can help act as a guide and reference for the progress.

enter image description here

The following 3D Viewport settings help a lot when baking.
Note: this is not a Material view setup, the texture you see here is the texture that will be baked to. If you export this model, you will not see this texture unless you first setup a Material.

enter image description here

Next we see an obvious error, often when things go this wrong you will find an nGon adjacent to the problem area which I think is what's going on with the main point of your question.

enter image description here

Now at this point we can consider the removal of the main center a mistake since it's removal was pre-mature; we have to work on both sides of the model to clear up the remaining UV Coord zero-area faces. We'll just call this a lesson learned.

Once you have the overlapping vertices selected, you can use s with your cursor over the UV Image Editor to scale them and give the faces in that area some space in the UV map.

enter image description here enter image description here

There are a few edges that overlap at nGon transistions which should be cleaned up. The baked texture will have errors at the areas.

enter image description here

Next is an animation that shows a quick way to deal will all those little circle insets. With them all selected, you can scale them all as a group and then move them into place one at a time using 'g' then circle select 'c' is used to remove the newly places areas from the selection, then grab again, then deselect...

enter image description here

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  • $\begingroup$ Whoa. Wow thank you for the very detailed walkthrough. It will help so much. $\endgroup$ – user2016 Oct 29 '14 at 20:23

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