Complex meshes get very dark after building light.

Hello guys,

I am desperately seeking some advice and help. I am working on a project for a while now. The goal is to take CAD files and present it in good quality in VR. What I have done so far:

  • I created a very low poly hall (picture two) where I have some rect light sources, a directional light, skylight, a BP sky sphere, reflection capture box and lightmassimportanceVolume.
  • Importet a postporcessVoluime and set the exposure to a fixed value of 1.
  • Then I importet die CAD files one by one with Nanite activated, assigned proper materials to it. I also auto generated UV maps for the meshes. I have two pictures from one mesh with both UV channels.

My problem:
As you can see in one picture, the hall itself is pretty good lit, but the mashines/meshes whith the materials on it are super dark - how can I fix this? If I review the meshes in the mesh editor, they look pretty good lit. Even though the resolution of the texture of the metal seem to not work…

Is it possible that this is related to my lightmap beeing this small as shown in the other picture with UV channel 1?

Can anyone give me some help or tips?

Thanks a lot!

All the best,
Patrick





You’re not going to get a good bake with lightmap UVs like that, even with a 4k x 4k lightmap. It’d take forever and still not provide enough lighting information. You can try relying on the volumetric lightmap for that particular asset. Volumetric Lightmaps | Unreal Engine Documentation

In essence, you cannot rely on the engine to generate lightmaps.
Not for complex model, and not for simple oness too since it doeant take into account texel density and a bunch of other things like power of 2 pixel scaling.

Take the model to something else - other autodesk stuff probably?
Or Blender.

From there, you slice up the model into parts that make sense, and generate lightmaps for it manually.
Possibly on a base power of 2 textures that is around 1024px^2 and no larger.

You align each UV island vertex to the center of the pixel it sits on, so as to have clean bleeding when you mip the texture up and down.

The end result at that point is a model with a set of UVs that works across anything you push them onto. Regardless of the size you pick when baking.
Remebering that 1024 is probably the minimum size you want for lighting anyway.

The more pieces you separate out as different meshes, the better quality of a light bake you end up getting.

But as you do, you need to keep track of the texel density of the UV map, and always keep the pieces at the same scale, so that the light bake process doesn’t jump in quality from one object to another, but is consistent acrosd the board.

Hello guys,

thanks a lot for your answers and input! I feared that the problem might be the lightmaps but I hoped it wouldn’t :laughing:
The volumetric lightmap is a good advice but I am already using it. I played around a bit with the settings but couldn’t get any improvement.

As you said, if I am cranking up the lightmap resolution it gets a bit better.

Now I have importet all the meshes from FBX files. I tried to import the STEP file as a whole via Datasmith where I got every single part as mesh. The problem there is that the performence then is poor even with Nanite. I will try to play around with slicing up the mesh and see if the results getting better.

As it soon will become a time problem - is there any other way to improve, even slightly, my outcome by adjusting some other settings?

Thanks again!

Best regards,
Patrick