UVs, Texture Sheets and Texel Density - How the hell do I texture this big ol' thing?

RedSaturnSix

Hi folks, I'm quite new to 3D but I've modeled a few individuals objects.

However, now that I've started work on a larger scene project, I've run across issues with texel density. The plane in the attached image is a 512x512cm object with a 4k texture applied (i'm using UE4 where a cm is 8px). 

Now my problem is that the large metal girder here that makes up a piece of the building around which my scene takes place is far too big to fit onto a single UV sheet while also maintaining the desired texel density.

How do you as artists maintain your texel density of assets larger than your reference object before bringing them into suites like Substance Painter?

TL:DR How do I split up an objects UVs onto multiple texture sets in a way that facilitates seamless texturing in Substance Painter?

ant1fact

You don't really split up your objects into multiple texture sets, not in this case anyway. What you do with large objects like this is you use a tiling material on it, scale up your UVs until you got the desired texel density and then use mask in engine to blend with another tiling material (or multiple ones) to break up the repetition. No reason to use 4k textures, 2k should be plenty for all your tiling materials.

"(i'm using UE4 where a cm is 8px)" this doesn't really make sense if you think about it. 8px could be a cm or it could be 10m in the game world. Change px to tx, it makes sense again. Also it's entirely up to you what you choose for your texel density.

RedSaturnSix

Thank you, I was just going based on what I have read elsewhere. I actually assumed it was done with tiling materials and masks originally but research on the internet told me otherwise. Do you have any suggestions for tutorials or examples of this method and substance you can point me towards? Many thanks. 

ant1fact

I will give you some pointers for now as I've actually got to catch a train in like half an hour and this is a dense topic, but here's what I would do in case of that girder. There will be a lot to research but I think it will be more exciting for you that way anyway.

1) Model your girder with either support loops added to your hard edges, or using a single bevel and face weighted normals. You will not use a high poly for baking and you will not use a normal map for making your hard edges look rounder so you need either support loops or face weighted normals

2) If you want to blend between materials, e.g. want to create masks for specific damage around the edges, in cavities, etc. then unwrap your model in 0-1 space. If you are happy with just a single tiling material across your entire or blending between materials with some vertex painting down the line, then feel free to go outside 0-1.

3) If you chose to stay inside 0-1, then take the girder into Substance Painter and bake support maps using your low-poly as the high poly. Generate some black and white masks to your liking and export these for later use. Your work in Painter is done here. Generally painter is used for uniquely textured props

4) Create tiling materials in substance designer, or straight inside unreal engine, or just grab some from substance share and generate some bitmaps using substance player

5) https://docs.unrealengine.com/en-us/Engine/Rendering/Materials/LayeredMaterials

The benefit of this is that you can use a similar approach on a differently shaped girder or other elements in your environment while still using the same tiling materials. And VRAM is still a big consideration in optimisation so it should never be overlooked

Hope this helps and good luck!