Hey there!
Thank You for all the quick and helpful answers.
Unfortunately group to udim tiles method is not the solution to my problem.
I try to explain it a bit more detailed.
Image that I have multi poly islands, and those poly islands had multi uv islands.
The only condition i want to tell to the packer is which uv islands should hold together.
But i don’t want to bother which item is getting on which udim tile.
I have only 2 priorities here overall:
1 - uv islands on the same poly island should stay on the same tile (i understand Groups making this)
2 - Pack all the uv islands the most efficient way to achieve the best uv cover per tile (and of course take attention to “rule 1” during the process), and of course keep the texel density (or if i set manually different texel density ratios the packer should consider that but i already know that ratio based scale stuff)
Now i can sort out uvs to tiles with constant texel density, but one poly island can contains multi material id (if poly island has multi uv islands) because packer is not considering the uv island to poly island relation.
As i can see Groups simply sorting out the groups to different udim tiles (and yes i see there are lot of options but none of them is covering the option i need above.
Please let me know if my explanation is still confusing 