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Can't create second UV Channel with overlap UV


I know there are similar questions already asked and I have read them all, unfortunately those questions are specific to those people's projects and don't reflect mine. I have several issues I am trying to resolve and I hope someone can shed some light on them because this is stalling my progress greatly.

First off, I am new to game design in general, I have been working in UE4 for about 6 months and I haven't used any 3d modeling program for any of my work. I tried using Blender but the guy who created it must be left-handed and have eyes like a flounder because I find trying to do anything in it extremely frustrating and backwards. What I have been doing is making my static meshes with UE4's geometry shapes. So far I have done really well with it and have made some really nice looking things without issue...Until now.

I created a dumpster (see screen shots below) and to me it seems very basic. I did it using all geometry shapes and turned it into a static mesh. When I placed it into my level and built the lighting, I get an overlapping UV error. As I do with all the mesh's I have made this way, I go into the mesh editor and create the second UV channel and it always works for me and solves the issue, but for the dumpster, it will not let me create the UV channel. I changed it to 1 and it doesn't create it. After reading about people with similar issues, I figured that it was because the dumpster lid wasn't close enough to the dumpster and was creating a small gap too tiny for the UV channel to be created properly. I then remade the dumpster again making sure there were no tiny gaps to mess it up. After finishing that, I created the second UV channel for the new dumpster and it saved it, however it still tells me I have overlapping UV's and a new error "lightmap UV are overlapping by 2.8% Please adjust content-enable error coloring to visualize" I enabled the error coloring and it does nothing to show me where the issue is.

So here are my questions:

  1. Why are the dumpster lids coming out as a grey blob when placed into the level instead of looking like they do in the mesh editor?

  2. Is there a way to insure I wont have lightmap UV's overlapping when creating my geometry shape items before turning them into a static mesh? (from what I have found in research is that I can't undo a static mesh unless I use a 3d modeling program, which I am not).

  3. WHY or what causes the UV's to be overlapping in a lightmap? (I have made several items using the geometry shapes with much more complexity than this dumpster and haven't had this issue before.)

  4. What caused the first dumpster I made to not allow the game engine to create a second UV channel? Was it because of the tiny gap between the two shapes?

Please see photos for examples.

This is what is supposed to look like

alt This is what happens when I place it into the level

Product Version: UE 4.19
dumpsterpic1.png (917.7 kB)
dumpsterpic2.png (759.9 kB)
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asked May 16 '18 at 06:11 PM in Using UE4

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avatar image aranfistaleno Jun 16 '18 at 07:34 PM

hello i have a probleme in the same contest but my mesh was made in sketch up and is a bit too complicated, blender won't open it it crashes evry time but, when i made UV's suing unreal , when i create the first channel it seems all good everntho it's darker when i build lights, but when i create the second one, the UV 0 becaumes a mess : https://cdn.discordapp.com/attachments/337290865326292992/457616900390912040/unknown.png and this is uv1 : https://cdn.discordapp.com/attachments/337290865326292992/457617360120184843/unknown.png

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Hi Meious!

  1. I belive this is because you have the editor in UNLIT lighting mode (select LIT from third dropdown on the top left of the viewport or ALT+4).

  2. Not that I know of. But keep in mind that when you autogenerate UVs Unreal will not create any new seams or splits or do any relaxing/pelting on your clusters. It will simply take the clusters already defined by Source Lightmap Index and repack them in Destination Lightmap Index in a way that eliminates/minimizes overlap. It can be possible that some UV vertices are being welded together in an undesirable way during conversion to Static but honestly a 2.8% overlap is not bad given your methods. Can you open up the UV visualizer in your mesh editor, set it to the second channel, and post it please? I can try and help you identify overlaps this way.

  3. This is hard to explain thoroughly if you haven't used a 3D DCC but the short answer would be: not manually unwrapping your UVs in a 3D app is what causes your overlap. If you're apprehensive about jumping into a 3D DCC you can check out Unfold3D - made explicitly for unwrapping and has a 30-day free trial (and excellent packing algorithms). Using it on an FBX export of your meshes while following their youtube tutorials will definitely help you undertand what's happening behind the scenes.

  4. The only times I've had this error was when there was no UV info on the Source Lightmap Index, does your original mesh have UVs in Index0?

EDIT: PS: Proper polygon modeling with subdivision workflow is in the Engine's development roadmap. Once we get that I'm pretty sure it will come with actual UV solutions.

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answered May 16 '18 at 08:27 PM

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