[UE 4.5 Preview] Auto-generated lightmap UV, has overlap

Well I don’t know, if it’s known bug, just want to mention it.


I’m definitely curious about this one since we’re working to make lightmapping that much easier starting with 4.5.

I’ve used it a few times with meshes and haven’t noticed any overlapping UVs. Is this a simple mesh like a wall or more complex object?

If you can show a image of your asset and the UV 1 that was auto-generated or can provide an asset that causes this error I would certainly like to replicate this and get something like this fixed as soon as possible.

Thank you!


Link to this mesh https://www.sendspace.com/file/4m89e3


Thanks for posting the asset for testing. That is definitely appreciated! :slight_smile:

There are a couple of things to remember with the new Auto-generated UVs method.

  • It is still being developed by Brian and there are changes that will likely be coming in the future to make this a much more fluid process.
  • And most importantly, as noted in the original forums post by Brian, the UV pack is generated based off the UV layout in channel 0 for the Diffuse.

With your asset you have cylinders for the legs of the table that are not split. This is where the overlapping geometry from the LM is coming from. The auto-generate UVs will not pelt or split this.

As an example I did a rough split saved the FBX in 3Ds Max and reimported and did the auot-generated UVs. The result was no overlapping UVs when building lighting.

Here is the the FBX if you want to see for yourself. As I said, It as just a quick rough and cut to split the cylinder edges.



I’m pretty happy to here it will get better. I Currently have a bunch of models I’ve purchased online getting the error in unreal engine 4.5 “object has wrapping UVs”. They look great until I build the lighting. I even tried importing to 3DS Max, re-exporting as FBX 2013. Still that same message. They import fine into unity, no issues. Before (pre 4.5) I was able to generate unique UV’s to resolve the issue (As long as the model didnt’ have too many polys or else I got D3DXMesh Error) Just wanted to give you a heads up.

Also, really wishing this feature was added to make my life easier importing these models like it was in Unity Imgur: The magic of the Internet

If you’re purchasing assets from any source other than the UE4 marketplace you will more than likely have to deal with this as most model sites do not have standards set for requirements for being “game ready.” You will need to clean up the UVs to account for this. Exporting as FBX 2013 vs 2014 you will not see a difference for the UVs.

The reason it worked before with the generated UVs was that there were two methods. Now there is only one within UE4.

The first method would be to unwrap the model, but it wouldn’t cut seams or do so right. This would result in stretched UVs and artifacts for the Lightmap. The second method (the one now used in 4.5) is to base the UV off the UV separation from the Texture UV (UV0) and repack them. If there isn’t a good setup it will still look bad which is probably the problem you’re seeing with yours.


This bug has recently been fixed and will be in 4.7. You can test this out with the 4.7 preview builds that are currently available via the launcher or once the final build of 4.7 is released.

The fixed CL is 2400339.

Thank you!


‘source other than the UE4 marketplace’? what? I bought Military Pack from martket place and the thing is that many stuff, not only from this package, is not production ready. Still, even on 4.7 I can not autogenerate UVs on truck from the package I have mentioned on the begining, I got crashes everytime. Actually I’ve already mailed to the epic staff about all those ‘production ready’ content from marketplace. The only answer I got was that they can give me a refund. So instead of getting high quality content or at least working with the engine we get ‘whatever’.

@EnOnE Masta - You’re right with that one. I’ve just grabbed this content from our depot to test and sure enough I’m seeing the same with the crash. While I think the original issue with crashing very regularly has been taken care of there may be some additional things with more complex objects that is still causing this to crash. I’m putting a ticket in for this and also reaching out to the content team to discuss this with them as well since there should be a lightmap for these vehicles since they’re not skeletal meshes.

I’ll update once I know more. Thank you for taking the time to point this out. :slight_smile:


I’ve passed the information about the Military Pack to the Content Team. The earliest they’ll be able to review would be next week.

With the truck asset m923_lod_000 I was able to get the crash, as stated earlier, with 4.7’s final release. I then tested this with our latest QA approved build from a couple of days ago and the crash is no happening. The lightmap is being generated with this object. This appears to be fully fixed for 4.8’s release. I’m sure there may still be instances where something can cause a crash and if you run into any I’d be more than happy to take a look and investigate.

Well hmmm should I point here all meshes or send you a msg? I have more comments on some other packages. The worst thing is that when I mail creators directly they do not care, and they often say that they will not correct any packages.

I’ve brought this up to the Content Team Lead. He has just sent you an email. Thanks for reporting any issues you have! :slight_smile: