Am getting strange lightmap artifacts that seem to follow polygon edges, can someone offer some explanations?

Hey there everyone! I am sorry if this has been covered before, but I could not find any info on it. I am getting lightmap artifacts on several of the objects in my scene that look like bleeding from another part of the map as they follow the edges of polygons in my meshes. The weird thing is these edges are in the middle of welded UV islands, so there should be no bleeding coming from other polygons on the mesh. Also when I view the mesh in Lightmap density mode, the lightmap densities are way off from each other even though the UV island is all welded and relatively uniform. I have been racking my brqain on this for a few days not and have not come up with anything, any help would be most appreciated. Thanks!

Here are some screen shots of what I got going on:

Here are the thin artifacts on my mesh:

See how they run along polygon edges:

Here you can see how the lightmap densities are all off from each other even though the UV island is pretty uniform:

Here is my static mesh settings:

And my global Lightmass settings:

And I have also tried this with the Lightmass indirect lighting quality turned up to 4 and I still get these artifacts. So if anyone has seen this before and knows how to fix it, I would be most appreciative of you for sharing the info with me. Thanks everyone and happy building!!!

I see you’ve got three UV channels. Presumably that’s one for texturing and one for the lightmap, but I couldn’t help wondering what the third one was for.

This might be too obvious, but are you sure you’re using the right UV channel for the lightmap? If you’ve selected the wrong map, and it has a break where the artifact appears, it could explain what you’re seeing. I’ve had that kind of artifact where the islands are packed too closely together, resulting in bleeding between adjacent islands.

Yes there are 3 UV channels, Channel 0 for texturing, Channel 1 which is my custom Lightmap UVs, and when those produced the artifacts, I had UE4 auto create an additional UV channel for lightmaps to see if their auto lightmap UVs would be any better, they were not better, they produced the same artifacts, but worse. The UVs you see in the image is channel 1 which is what the lightmap index is set to. Thanks again for any insight to this issue!!!

Actually another thing to check is that you don’t have any mesh oddities where the artifacts are appearing: normals pointing the wrong way, duplicated vertices, stray faces inside the mesh, and so on.

Hey everyone, thanks for the info. I have checked all the simple things, normals are fine, no duplicate faces or verts, lightmap index is pointing to the correct UV channel, etc. So none of that worked, but I did find a way to fix it . . . kinda . . . sorta. so when I export those meshes as FBX files to bring into UE4, I get the weird artifacts, however, if I export the very same meshes as OBJ files and bring those into UE4, the lightmap artifacts go away when I build lighting. That leads me to believe that either I am exporting FBX files with the wrong settings, or FBX files just SUCK!!! Has anyone seen anything like this before? Or any UE devs, if you read this, are there issues with FBX vs OBJ files that you are aware of? Below is a screen cap of my FBX settings when I export. Do they look right? Any info would be most appreciated. Thanks everyone!

incredible! the most critical topic about the future of UE4 and sitting there unattended…