Using reimport does not change lightmap uv

kurylo3d · February 9, 2017, 2:09pm

I just noticed that right clicking a static mesh and hitting reimport does not actually give you new uvmap 1…

If i do an import from scratch and overwrite the mesh with the same fbx file… only then it will actually import the new uv map from that fbx.

Obviously its not a show stopper, but something definently worth looking into for developers.

anonymous_user_0c62419a · February 10, 2017, 4:21pm

Hey Kurylo3d,

I tested this with the following steps:

Created a simple cube in 3dsMax and Edited UV Channel 1 and UV Channel 2 (in 3dsMax it starts from 1 and not 0)
Imported into unreal (made sure that generate lightmap UVs was unchecked)
Opened the cube and looked at both channels in the viewer.
Went back to 3dsMax and changed both channels again then exported so that it overwrote the cube mesh fbx
Went into Unreal and reimported the static cube mesh.
Opened the mesh viewer and looked at both UV channel 0 and UV channel 1

After this test I confirmed the reimport was working as expected and the UVs were updated accordingly. In your modeling application it can be easy to not include the edited UVs. For example in 3dsMax if I change UV channels without collapsing the stack the edits I made to the original channel are lost.

Let me know if that helps,

Ed

kurylo3d · February 10, 2017, 5:25pm

I think you misunderstand. “Reimport” does not change the uv channel one to the current state of the fbx file… but regular import and overwrite works correctly. Both instances are using the same fbx file so it cant be anything to do with the modeling package… (maya by the way) And I always delete history.

This happens to me so often that i dont even bother using reimport unless its a quick geometry only change… I always make sure to do regular import and overwrite… Cant trust the other method.

anonymous_user_0c62419a · February 13, 2017, 3:38pm

During my test I used the “reimport” feature. After doing this the UVs for all the channels updated correctly. I didn’t attempt to import the mesh normally and overwrite.

It may be possible that your source file path got messed up. This can happen if the reimported mesh is in a different file location than the original import or if the source file path is lost.

You should be able to see the source file path if you hover your mouse over the thumbnail and it will say at the bottom of the tooltip.

Zombie · August 9, 2017, 12:02am

I can confirm that reimporting doesn’t update the UVs for the lightmap. I think this happens if you have initially imported the mesh with auto UVs then tried to change it to not auto generate the UVs. I edited the mesh so I saw that the import paths were correct.

Every time I uncheck Generate Lightmap UVs and reimport, it checks the box back so you can never not have that box checked.

Night_Watcher · November 19, 2017, 3:58pm

I can confirm that this issue is still in 4.17, just do what @zombie said to replicate, can we please get a bug report for it, this has been a pain that I keep countering in all my projects.

anonymous_user_9edaed59 · November 30, 2017, 12:50pm

I can confirm that too…I always use to generate the lighmaps in unreal as i import my geometry the first time…when then i notice that in some geometries it gives me some errors as i build the lighting solution, i then edit the uvs in my 3d packet…export again and overwrite the same file…then i reimport the geometry with generete lightmap uvs unchecked…but the uvs remains the same as before…they do not update…has anyone find a solution?

anonymous_user_9edaed59 · November 30, 2017, 12:50pm

I can confirm that too…I always use to generate the lighmaps in unreal as i import my geometry the first time…when then i notice that in some geometries it gives me some errors as i build the lighting solution, i then edit the uvs in my 3d packet…export again and overwrite the same file…then i reimport the geometry with generete lightmap uvs unchecked…but the uvs remains the same as before…they do not update…has anyone find a solution?

script526 · June 11, 2018, 7:55pm

Oh man. Just a few days ago I noticed why is there incorrect UV map on one of my meshes. I remember that I replaced it before. And now I encountered accidentally with this topic. And found the answer apperently))

anonymous_user_57d69625 · June 11, 2018, 7:42pm

I had this problem too. The my texture UVs updated fine, but the light map UVs would not update. Unreal was just using it’s own auto generated UVs.

My solution is in the mesh’s details panel. There are 2 “Generate Lightmap UVs” check boxes that need to be unchecked. One is under the Import Mesh settings and the other is under the LOD 0 Build settings. After unchecking the one under the LOD hit the Apply Changes button. Once both are unchecked, hit Save and close the window. Re-import your mesh and it should have worked.

I did this in 4.19, but it worked for other’s using earlier versions of Unreal as well. Their button layout was a bit different, but under the same categories.

Bazicproduction · November 5, 2018, 8:23am

THank you so much Ant Thief

macoll · May 17, 2020, 4:50pm

Hello,
I confirm, we have to uncheck under LOD0 aswell if we want to reimport a model with a handmade lightmap. So we have to uncheck under both LOD0 and Import Settings in the details panel of the mesh ^^