Extreme Overlapping UVWs causing lighting issues

I have an issue when trying to use a model of mine and light it in the Unreal engine. It states that the lightmap UVWs are overlapping by a small amount - 1.1%. This number has bounced around depending how I manipulate the UVW, from 1.1% to 98% when I try to relax it. Below is my UVW map with overlap highlighted in red - doesn’t look like 1.1% to me.

“Low” Res:
uvw low res.png
High Res:

This is causing lighting defects for me in the engine. Or, at least I believe this is the problem, as messing around with the UVWs is changing my problem in-engine.

This is what the problem used to be. Note that the light source is where the Move gizmo is (at this point, overlap is said to be at around 8-9%).

lighting issues.png

This is my problem now that I have shrunk down the UVW to fit within the 3ds Max checker box:

lighting issues2.png

Still problematic, but a little better (1.1% overlap… apparently).

So how do I fix this issue? There’s no way I can manually remove overlap for all of the UVW - that would be a nightmare. Anyone have any recommendations?
Here’s the FBX file:

Thanks in advance y’all, I’m really stuck here.

Hey domportera, this is what your second UV map looked like in 3ds:

I’ve used the steamroller script and it popped out this in just a second:

How are you unwrapping your meshes?

Wow, you certainly made light work of that. I unwrapped using the Unwrap UVW modifier. I was looking at the first channel though. Why would the first channel be so screwed up while the second channel looks great? And how would I prioritize use of the second channel over the first in the Unreal engine?

Also, I assume the steamroller script was acquired online? (SteamRoller | ScriptSpot) and is there any way of performing that flattening without it (that wouldn’t be horrendously tedious)? Sorry for all the questions, I’m new at this if you couldn’t tell.

No worries, I am new to this as well.

The first channel is for your textures, it can overlap the UVW ‘square’ in your Unwrap UVW modifier, if it does the textures will just tile.

After you unwrap it once, you can apply another Unwrap UVW modifier, and change it to channel two. There will be a pop up that asks if you’d like to move when you have in channel one to channel two, or if you want to abandon it and start on channel two from scratch. If you’ve already spent the time unwrapping channel one for your textures and nothing is overlapping you may as well just move it. But if you want to flatten them yourself you just select everything and go up to mapping > flatten mapping


Then hit okay in the flatten mapping dialogue, and it’ll flatten everything for you.


This is what the steamroller script does, except you can do everything all at once, just make sure it is on channel two.

Another thing, when you’re importing them to Unreal make sure you un-check the ‘generate lightmap UVs’, or it will make a third channel and try and use that.

I hope this makes sense, I spent month and months trying to wrap my head around unwrapping so don’t hesitate to ask questions. I can try and answer the best I can while the learning process is still fresh in my mind.

One more thing to add to James’ explanation. When you first import mesh with no lightmap uv’s in the second channel, Unreal will automatically set Lightmap coordinate index to 0. After that, even if you generate 2nd channel uvs in max and re-import, it will stay set to 0. So go into static mesh editor, make sure to change that to 1 instead and save your mesh.

Thanks a ton James! I did the flattening and it worked great. and Brick that tip was invaluable as well, I just deleted the asset altogether and re-imported without generating Lightmap UVs.

I’m gonna keep this thread about in case I run into any other similar UV problems