Straighten UV island of more complex objects (Blender 2.81a)

[Vitus]

Hi guys,
I’m fairly new to Blender, so please forgive my ignorance. I am currently working on a radial engine and started UV mapping some of the parts. It went really well and faaast, I’m really impressed so far. But I stumbled upon this roadblock and couldn’t find a solution online yet.

I have this part here, it’s the intake manifold/supercharger:

I want to unwrap the center part of this geometry and set up the seams accordingly. The result however looks like this:
(sorry, can’t embed this, due to new-user-restrictions), here’s the link:
https://i.imgur.com/urUrmLa.jpg

I would like to straighten the uv in a way that the vertical sections are parallel. I tried the “follow active quads” method, but because of the intersections in the mesh, the result is even worse. There’s also some triangles in the mesh, which don’t get touched by that method anyway.

Besides doing it manually, can you think of a way to straighten out my uv?

Cheers,
Vitus

[graeme_h (Graeme Harvie)]

Check out an addon called “uv squares”. I haven’t used it myself but check out this video. Hope it helps.

uv squares

[Vitus]

Thanks for the tip! I gave it a shot and here’s the result:

I’d say it’s much better than what bare-Blender came up with, but I’d say it’s not quite there. I think the issue is that this addon squares everything and as a result the intersections don’t map right.

One way I think this could be solved is by defining constraints to the uv and then let an algorithm figure out the rest. So in this example I would straighten out the furthest left and right colunm of faces, constrain those and then run an unwrap algorithm that squeezes everything in the remaining space. Does something like that exist?

[ajm]

What do you want to UV it for? I mean, if you have a certain material in mind, these parts usually do better with a procedural approach for the overall material, then you could use a smaller area, say like the flattened portion as a part that you could throw into a UV for things like labels/decals and such.

[Vitus]

Same answer as in my other thread over here:

UV workflow practices for complex hard-surface models

Thanks for the quick reply. The asset is for flight simulator x/prepar3d and the outdated 3d engine of both platforms puts some limitations on the model. For instance one thing I found out years and years ago is that the platform performs way better using fewer, but larger textures instead of lots of smaller ones. Procedural material is out of the question as well, since the engine doesn’t support it. The same is true for a lot of modern functions, like UDIMs. It’s not supported by my platform, …

I’m working with an older platform that doesn’t support any fancy material.

[ajm]

Understood, This will be a pain to do for complex shapes, and unfortunately not look very good, map wise. So do they allow simple cubic projection mapping around the model? I mean that stuff was around before UVs, or is everything required to be UV mapped? I was looking around the prepar3d site, but couldn’t find the answers. Looking, found the texturing part…

[Vitus]

In order to get the model into the flight simulator, you have to use an exporter. The exporter converts the model first into the x-format (old direct x file format for 3d models), and from there a script exports it into a native .mdl file. The mdl contains the geometry, animations and animation code segments and a list of material properties. The textures need to be provided separately as dds files.
In principle, you can get away without a uv map by giving parts of your model a uniform color, but it always looks crap in the sim. If you want things to look nice, you have to uv map and texture the part.

[Vitus]

btw. the new node-based materials of Blender screwed up a lot for fsx/p3d and x-plane developers, because now none of the exporters work anymore and have to be re-written. It’s a tedious process, check out this if you’re interested:

Blender 2.81 and FSX/P3D Toolset

[ajm]

The part that you are wanting to unwrap will not be easy, but you can unwarp, do the procedural thing I was talking about and then bake those textures onto the UV to limit distortion. This part is in an area of obstructions (?) like a cowl and rotor and prop I assume, and fantastic detail may not be needed here (though I know you want there to be…I get it) since there is a lot of other things to visually break up the part, as well as lighting and shadowing. How old is this engine? I haven’t heard talk of using psd files for textures in a long time.

[Vitus]

I think I understand your suggested approach. But I don’t think I can go with that, I really like to unwrap everything
The reason why I model all the engine accessories in the rear of the engine in the first place is so I can reveal them when the cowling comes off, so having a proper uv map even with those part is kind of essential. Besides, this won’t be the only part of the aircraft where I have this sort of issue anyway. So whatever I take from this, I’ll apply to other parts of the model as well.

I couldn’t locate the type certificate of that particular engine type yet, only found supplements. So I’m not 100% sure on the date, but I think it must’ve been from around 1933/34. It’s a Pratt & Whitney Wasp S1H1-G.
And about the psd texturing: I really enjoy that part, it’s a lot of fun to create textures that way. Very similar to painting a plastic model.

[ajm]

Could you just post the object you want unwrapped and I’ll take a crack at it if I can keep my daughter off my lap long enough?

[Vitus]

You got it! Thanks for taking your time and say hi to your daughter!

manifold.blend (1.2 MB)

[ajm]

Added three loops of seams, one down the center line and two others around the edges to separate the problem areas. I did not arrange the islands so you can see the layout of just the central parts. If you run UV Squares to straighten things out, they should behave a bit better, and you can overlap the parts you want in order to save map real estate. I don’t know if this helps, but for me I would be happy. The complex surfaces wrapping around the base of the exhaust in the recesses are the big issue.
manifoldv2.blend (1.3 MB)

[Vitus]

Thank you for that, it really helped! Adding more seams seeeeams to be the trick here. I always try to create coherent uv islands to make the painting process easier, so adding more seams is counter-productive in that sense. I implemented your approach a little differently though:

That gives me this after unwrapping:

I can now use the suggested “straighten UV” toolset to normalize the round shapes and then move the connected islands together:

The last step will be to stitch the uv edges together to generate one big mesh again.

It’s not a click-and-forget solution, but I think it’s straight-forward and quick enough to deal with this sort of geometry.

@ajm, thank you so much for your time and effort, this really helped!
@graeme_h, thank you too for the suggestion! I think I can make good use of this addon!

[Vitus]

End result:

[graeme_h (Graeme Harvie)]

You are so welcome. @ajm provided some great info

So nice to see people appreciating other people’s time and effort.

A “thank you” goes a long way!!

Take care.

[ajm]

I didn’t do the UV squares tool, so you could see what it actually did, but I thought this approach would get you much closer. I tried quite a few configurations, but those recesses were quite the bother. Glad I could help you out a bit.

[Vitus]

fyi, if you’re interested in an update, here’s the UV map for all parts of the engine: