Developer Notes

This is considered a non-issue as only the channel assigned to lightmap index are wiped. If you want to maintain hand tailored UVs generate lightmap UVs to use as a throw away channel.


The merge actor tool no longer saves additional UVs used for the merged mesh. This was not the case in 4.13, but in 4.14 and later this information is no longer present.

Also worth noting is that if the MergeActor Tool left Generate Lightmap UVs on in 4.13 it would set the lightmap as UV2 and still not wipe the second UV from the mesh with the multiple UVs. In later versions it would still wipe the 2nd UV from the model.

Working: 4.13.2 Binary CL-3172292
Broken: 4.14.3 Binary CL-3249277
Broken: 4.15 Automated Build CL-3269047
Broken: 4.16 Dev-Main CL-3273433

Steps to Reproduce

1. Open UE4
2. Import the attached Static Mesh with 2 UVs
3. Add the SM to the scene and add a copy or another separate mesh (one from the modes panel works as well)
4. Go to Windows > Developer Tools > Merge Actors Tool
5. Select the two or more actors in the scene
6. In the Merge Actors Tool disable "Generate Lightmap UV"
7. Click Merge Actors
8. Open the Generated Merged Actor and look at the UV's dropdown

Results: Second UV is no longer kept with the merged actors. Only the first.

Community References

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CreatedJan 26, 2017
ResolvedMar 10, 2017
UpdatedJul 14, 2021