UV Mapping - V (aka X) Centering of Islands / Vertices?

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Over ten years ago, when I was first puttering around with making my own 3D stuff, I learned a few things that were presented as This Is The Way for ALL 3D work. Of course, no they weren’t – useful as “good” all-quads is it’s not what 3D games use, and so on. One of those things was: if your UV map has an island for a symmetrical part of the mesh centered on a given axis, then “good” UV design requires that the island also be symmetrical, and its centerline verts be exactly centered on that axis. This allows for separate 2D software to more easily create a texture map by mirroring across the same axis. (Any asymmetry to be added later if at all.)

The usual example was a human mesh, left-right symmetrical – the UV-mapped head and torso islands centered on the V (aka X) axis, every centerline vertex in them exactly centered on that axis to the most decimal places the software supported. The limbs and such might be mirrored across the axis, or scattered around the remaining space in a denser packing scheme, but the head and torso islands were always given exact X-axis central pride-of-place in any “good” UV map.

Blender’s Human Base Meshes Asset Bundle, assembled from the contributions of various volunteers, has some UV maps that follow this principle and some that don’t. I recently suggested that Suzanne’s upcoming UV map follow this principle – when writing that topic it would’ve been helpful if I could’ve cited documentation, tutorials, posts, etc, however old, recommending this methodology.

I can’t find any. Like, not anything. I don’t remember where I learned this, I’ve looked everywhere I can still get into that I was on back then, I’ve gone over TurboSquid’s best practices again, I’ve googled and asked the duck with every search term I can dredge up. :confounded: I’ve got nothing.

I can understand it’s been depreciated! Innovations in both 2D texture creation and 3D baking make it a lot less important than it used to be. But it’s not just a fig newton of my imagination – people are still doing this, they had to have learned it somewhere, right? :face_with_raised_eyebrow:

So, anybody out there? If you do/did this, and remember where/when/why/who/whatever? I’d appreciate it if you’d let me know. :pray:

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Speaking for myself, if the UV island of a symmetrical piece of geometry is not symmetrical too, I’d simply consider that bad practice. Texel density on one side will be slightly different then on the other, even though it may not really matter much in the end. Which is nothing that I learned or picked up somewhere, it’s just common sense.

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How about looking into videogames assets from early 00s. GTA3 is the first one that comes to the mind.
image
The main reason for symmetrical UVs was that you could simply overlap them and paint only one side.
The amount of times it was done this way is the whole era of games made back then and being made today as well. Not to mention usefulness of this with vehicles and weapons, for example. But there wasn’t any particular holy bible on UV. It was, as Bassig said, a common sense, usually related to certain specs of the pipeline - we had to cramp in as much as possible with small amount of disc space.

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I agree with the above comments- I’ve heard this anecdotally in the context of making games but I’ve never seen a hard source for it. My guess would be that this is a “best practice” passed down through the game industry, back in the day, by word of mouth, that leaked into the broader 3D world

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I see this type of layout of when googling facemap textures and face scans, but not a lot elsewhere. Maybe it has roots in old headshot photo to texture techniques?

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This is the kind of thing (with significantly older UIs, of course) I remember:

screenshot.2023-07-20 21.08.900x
screenshot.2023-07-20 21.08.900x900×900 255 KB

I’m not saying that the technique you’ve shown isn’t related, might even be a precursor. A little of what I was doing involved game assets, so maybe. And I appreciate what everybody’s posted so far.

But I remember this being explicitly discussed – not in the exact terms I used above of course, or you’d think I’d’ve found it already. I was hoping for something more citable than variations on “it’s so obvious that’s the best way, don’t think anyone bothered to mention it”. :cry:

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Ah, this kind of symmetry. Yeah, never seen an explanation for that. Then again this could be a waste of UV space. The roots could be anywhere, to be honest. But the main reason for that definitely lies in the need to texture in 2D editor, and with more “readable” layout it’s way comfy to paint.

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Its just something from the old days. Nowadays nobody* drawing textures in “Photoshop”, so nobody really care about symmetry that much.
Basically any good software for unwrapping will make anything symmetrical just by default in case it can be symmetrical at all. Most of the time only one thing which you should do is to align unwrapped island horizontally/vertically.

Specifically for human heads, my thougths: you can search some videos how people make highly detailed models where they take some height/roughness/specular maps captured from real humans in a special fancy photo rigs. It would be much easier to match scanned textures with yout original model UV if those UV are symmetrical and aligned in UV space. I saw something about it on the videos maded by creators of ZWarp software. I bet you can find those video on youtube.
Everything else related to symmetry are just a matter of technical aesthetics.

*Actually someone are still can use photoshop or krita for textures. But amount of those artist are really small and mostly in handpainted textures area. And most of those people working in 3DCoat.
You can find some really cool and ultra realistic texturing doned in photoshop in Artstation, but its not how its made nowadays in the industry.

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Yea, this is just one of the unspoken rules of 3D

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Modding TES IV Oblivion was what got me into 3D in 2006 / early 2007. Pretty much every armor or creature back then had mirrored UVs. Totally made sense back then considering video memory and workflow limitations (creating textures in Photoshop or Gimp. Those long nights of manually drawing edge wear into textures, oh boy). Nowadays I’d rather avoid mirrored/overlapping UVs at it makes baking easier. As for UVs like in the image above, can’t remember having seen those a lot though.

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And again for the latest posts, thanks people. Don’t know if what I originally wanted this for is gonna get anywhere, but regardless I’m glad to hear I wasn’t just imagining it.

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