LOD Groups causing errors in Lighting Build - Overlapping and Wrapping UVs.

Development Rendering
1

Hi Epic Games, Hi everyone,

So bit of a problem here. I’m building my level with environment Static Meshes and the Static Meshes have auto-generated LOD Groups chosen during import. In this case, the Level Architecture LOD Group.

When I build lighting, I get very many errors “Object has overlapping UVs. Lightmap UVs are overlapping by 1.75%” and / or “Object has wrapping UVs.”

Now… My Static Meshes absolutely 100% certain do not have overlapping UVs in UV channel 1 in LOD0 - the base mesh. I am using UV Channel 0 for textures / materials and UV channel 1 for Light Maps and the Lightmap Coordinate Index is set to 1 for all the meshes.

The Lightmaps are auto generated during import.

I have even exported my Static Meshes to my 3D software and looked at the UVs in the Lightmap UV channel, and there are 100% definitely no overlapping UVs or UVs outside the UV Space.

If I change the Static Mesh LOD Group to None and then rebuild the Lighting, the errors are gone. So it is clear that the LOD Groups are causing errors in the Lighting build. Why?

Does anyone know why or how to fix this? Any help or advice would be very much appreciated. Many thanks! :slight_smile:

2

NOTE: I was using auto generated LOD Groups with Static Meshes in 4.14 and did not have this problem. Seems this problem has only started with 4.15.

3

Has anyone else encountered this same issue? Does anyone know why it’s happening or how to mitigate it? Thanks!

4

I have this issue as well, sometime (or most of the time) the auto UV for the Lod 3/4 will cause the UV run out of the “UV box”, auto lod seem will stretch the UV

I have to increase the LOD percentage to fix the issue

5

Hi Raventhebird - thx very much for your reply.

Yes, that’s what I figured, was that the UV Layout for the the increasing LOD groups, was causing the UV to go outside the bounds and overlap UV Islands. I guess at the end of the day it’s not that of a serious issue cos, the UVs are only overlapping by small amounts 1% or 2%. And all meshes build LOD level 0, absolutely fine.

You say that you are able to fix the issue by increasing the LOD percentage. Can you explain that a bit please? Thanks very much.

Really strange that this issue didnt occur with 4.14, and only seems to have started in 4.15. Thx again for your reply Raventhebird! :wink:

6

I means increase the triangle percentage, since the modern hardware is more tolerate to polycount, few percent of the triangles increase should be fine, and its the fastest way to fix it

7

Cool man, I’ll try that. Thanks a bunch! :slight_smile:

Neon Pool table is awesome btw! :cool:

8

The above mentioned issue has been FIXED in Unreal Engine 4.15.1. LOD Groups are no longer causing Overlapping / Wrapping UVs.

Thanks a bunch for fixing this Epic Games! You guys rock! :wink: