I am using Substance Painter for the first time and using Houdini to export UDIMs to it.
This is not really relevant for this project, since I don't need high-res textures.
But while exporting I wondered if the scaling of the different islands affects the resolution of textures in general, or when exporting to Substance or Unreal Engine for example.

I failed to recreate it, but before when I had the UV Layout Scale set to fixed, they all seemed to have the same UV scale, but some of the larger pieces where below 0 in the coordinate space, which caused issues upon exporting to substance painter.

Anyway, as you can see in the screenshots, the tires take up the same space as the airplane's body. So I am wondering how that might affect rendering in Houdini but mostly when exporting to other DCCs.
Or does it not matter when using procedural materials?

attach]UDIM_scale_maximum_viewport.PNG

Size of the uv island obviously matters for resolution of the baked texture
As for procedural ones it does only if they are uv based as the scale of the features would depend on uvs

Ideally you would just use udim attribute and a single UV Layout SOP to get all islands with relative scale to each other packed in corresponding udims, since if you are doing it in foreach loop you will get just relative scales within each island

Also if anything is packed in negative areas it means it was not possible to pack those islands

Thank you very much, I will try out what you said.
Edit: It took me a while to figure it out, but I got it now. Thanks