Lightmap UVs auto-generated

what i did:

  1. I imported a .fbx with overlapping UVs, but as you can auto-generate UVs during import i had 2 UV channels after import: UV0 bad and UV 1 fine.

  2. To get rid of the overlapping UV channel 0 i set “source lightmap index” to 1 and “destination lightmap index” to 0 then hit “apply”.
    this deleted the old overlapping UV channel and made the auto-generated now UV channel 0.

So i assumed, now I have only one UV channel, that seems to be fine and seems to be assigned correctly (see screenshot), but still get the error message after lightbuild “overlapping UVs”

what am I doing wrong here? is there a simpler way to fix a model that comes with a overlapping UV in UEd (not in the 3d program) ?

On the left middle area of your UVs, there’s very clearly a square with a bunch of overlapping UVs (along with a lot of other spots that need to be fixed). Plus, you have a bunch of completely wasted UV space on the right with what looks to be 1 polygon islands.

Fix your UVs manually in your 3d program. Unreal can’t save you here.

UE4 doesn’t really generate UV layouts, it’ll just separate and pack existing UVs to get rid of any stacking to create unique UVs for lightmaps.

For best results, unwrap your UV’s manually. Automatic mappers don’t care about continuity, they just split objects by the angle and you’ll get a mess like what you have there. I also wouldn’t model the keys of the piano individually unless you need to animate it, since it generates a lot of polygons, I’d bake that to much simpler geometry.

It sounds to me like you’re trying to overwrite your models original UV channel, and I don’t think you can do that.

Thank you all for you’re answers, but re-building all the UVs in 3ds max is too much work, so i rather dont use that model at all.
But as many available 3d models don’t have that non-overlapping 2nd UV channel I was wondering if there exists a tool or plugin to create it automatically?
The tool would just have to look at all the outer polys that can receive light and build the lightmap for the whole model (not for each single objects it consists of, nor the unseen/inner polys) in regard to the total dimensions. right?

There is steamroller (free script for 3ds max on scriptspot) that automatically unwrap/flatten in a single click. Works very well for non-organic shapes usually. If an object looks too complex for the script to make a nice uv unwrap, break your object into a couple of pieces and run the script on each separate part.

This is the lazy mode, it won’t give optimized results. You may need to use high resolution lightmaps sometimes to compensate.