Game Prop Workflow - Lightmaps & LODs

pom

I am confused about how to make these two work together. I've watched tutorials about how to make LOD meshes by deleting geometry within the UV islands but none of these tutorials mentions the lightmap UVs. When I'm creating the LODs my lightmap UVs just become a broken mess. Am I missing something here?

poopipe

In my experience LODs have always had unique lightmap UVs  (usually at progressively lower texel densities) even when sharing other maps

Mark Dygert

Simplygon handles it really well. You feed it a mesh, it crunches it and does all of the heavy tedious tasks. In some cases you can have it generate new UVs and it bakes some textures for you, usually not normal maps, those usually turn off as soon as the object starts to LOD.

At a certain distance, most object pretty much either stop casting shadows or stop having shadows cast on them or it's using a ridiculously simple mesh with an even simpler light map. 

Unreal uses simplygon and it pretty much makes creating LoDs almost a non-issue. I haven't made LoDs by hand in 5-6 years.

pom

@poopipe, If each different LODs have their own unique lightmap UVs, when lighting gets built in the game engine, how does the lighting follows up when switching the LOD? Do game engines builds a lightmap for every possible LOD?
@Mark, thanks I will check it out.

poopipe

The lightmap is just a baked texture and it needs to be unique for each instance of the object in the world. 

You can share the same uvs in theory but the systems I've used have all batched the baked lightmaps up with other nearby objects into large atlases based on lod level so there's no benefit to doing it

I don't know what ue4 does in this regard so it's probably worth reading up on it.