4.10.1 Auto Reimport loosing Lightmap UV

Just a quick FYI I’m getting a little bug in the UE4 auto reimport. I’ve got the importer generating lightmap UVs on some static meshes, when it auto reimports any changes to these static mesh’s UVs it looses the lightmap UVs that had previously been generated.

The bug is intermittent sometimes doesn’t occur.

Hey Jules86,

Could you provide me with some steps and the exact engine version you are working with (assuming 4.10.1)?

Just for your own information, we have put out three hotfixes since the release of 4.10.1, and your issue could potentially be resolved by updating to the most recent hotfix.

If you are changing your Static Meshes geometry in anyway new UV’s need to be created anyway, since those unque polys/tris unwrapped for the old model no longer apply to that mesh.

All you need to do is uncheck the ‘Generate Lightmap UV’s’, apply changes, then recheck the setting once you have re-imported.

Thank you,

Hi Andrew,

We’ve updated the build to 4.11.1 (we were using 4.10.1) and the issue hasn’t represented itself, however i’ll tread through the previous steps anyway.

  1. Static Mesh geometry and UVs (only one UV channel) were created in MAYA 2016 LT
  2. The Geometry was exported to FBX ASCII 2014/2015 from MAYA’s export selected dialogue.
  3. The geometry was imported to UE4 (10.1) with ‘Auto generate Light Map UVs’ set to true. (UE4 at this stage already had ‘Auto Re-import’ Enabled.
  4. Checking the Static Mesh would reveal that the Geometry and Custom UV (on channel zero) had imported correctly and that Light Map UVs had been generated on UV Channel One.
  5. Static Mesh Geometry or UV were then edited in MAYA 2016 LT and exported to FBX ASCII 2014/2015, overwriting the previous file.
  6. UE4’s Auto Re-import would then re-import the static mesh.
  7. Checking the Static Mesh would reveal that the Geometry and Custom UV (on channel zero) had re-imported correctly, however there would only be channel zero for the custom UV and now no channel two for any light map UVs.

Again it was intermittent so sometimes the light map would be fine.
Sorry I didn’t capture any screen shots to help with the process.


Well, we really appreciate the thorough steps you have provided even though the issue is not occurring in the current build. If the issue persists within current or future versions, please let us know.