newbie lightmap question

hey all
I’m having a hard time understanding how lightmaps work - I was under the impression that it is linked to the UV set of the object is that right?
Because if that’s the case how come all these shadows look the same when the uv set of the left most plane fills in the whole 0,1 range and the right most plane occupies a fraction of it
(light build quality if production)
I also heard left and right that you shouldn’t increase the light map resolution in the static mesh settings too much
in this next image - everything shown has it’s own UV set with all the light maps set to 64 but in order to get some decent shadows I have to increase everything to at least 1024
I saw on the realistic render example scene that the UVs for their floor mesh (which has very nice soft shadows with a light map res of 64) has a very large uv set in channel 0 - how does this come into play because I haven’t had any results on my end by scaling the UV set to cover multiple udims

I’m just trying to learn a proper light map workflow so any help and guidance would be really amazing

You are looking at the wrong UV channel, you are looking at UV channel 0, this is for textures. UV channel 1 is for lightmaps. You have to make a second UV channel in your 3d software to maximize/optimize the space for the lightmap. This is the UV for the lightmap on the realistic rendering floor:


BTW, in the realistic rendering example I have, the resolution is 128, not 64.

And most likely for your first test you didn’t change the lightmap UV’s, by default UE4 is set to generate a new UV channel to use for lightmaps.

There are multiple UV sets for a mesh. Typically, set 0 is used for mapping material/albedo/textures to the object, and set 1 is used for light mapping.
This is why set 1 needs to be mapped without ovelap, but set 0 can wrap as much as you want.
If set 1 is missing in the imported object, Unreal will generate a set for you. You can check properties on the object instance to figure out how dense Lightmass will make the texture for that UV mapping; you can edit the Mesh in the Mesh Inspector window to see what the generated UV set looks like.
If you would like a better UV set than the automatic set, you have to create it as a second UV channel in your source program, and map it the way you want it.

so the shadow quality is solely dependant on the resolution of the UVs on the lightmap?
What about movable objects with dynamic lighting - is there huge difference in performance/render time to switch to dynamic if it’s just an interior render for archi viz?

The quality no, there’s a number of things that contribute to the lightmap quality, though you can certainly improve the results with better lightmap UV’s

For dynamic lighting the quality is not as good as static since you can’t get the same global illumination results in real-time. If you’re not worried about real-time performance and want to be able to do things fast, then you can use Nvidia VXGI which will give you better dynamic lighting results without having to bake static lighting, though the results still aren’t quite as good as baked GI it’s better than the default dynamic lighting.

cool thank you all :slight_smile: