How would the lighting for this be baked?

melviso

Came across this:
https://www.youtube.com/watch?v=nTlG4dM1nNg

The artist is using texture atlas I am guessing, so he is using one texture for a number of repeating faces/elements which is really cool. Since everything is one model, how would one bake the lightmap using lightmass in ue4? Would the lightmap res have to be like 8k due to the model size in the scene relative to say a ground floor house?
or break it into smaller pieces and each piece uses like 2048 or 1024 textures?
Would using high res lightmap for a large model like this cause performance issues?
I intend trying out ue4 for archviz at some point so I am currently researching properly ( I have tried out ue4 before in the past tbh but found it lacking for archviz). I normally use offline renderers hence the question.
Thanks.

AtticusMars

Epic has a guide for unwrapping for lightmaps in their documentation. To answer your question yes, if you plan to export this as a single mesh you will need to crank up the lightmap resolution. I don't think 8k would be necessary, since lightmaps only hold lighting information they don't need to be as high resolution as your normal material textures and they can cope with things like stretching a lot better. But you'll have to run some test bakes with production lighting to determine for your self what you're comfortable with.

Regarding the performance cost, also from the UE4 documentation:

Using texture lightmaps with high resolution is the best way to get detailed, quality lighting. Using high lightmap resolution has the downsides of taking up more texture memory and increasing build times, so it is a tradeoff. Ideally, most of the lightmap resolution in your scene should be allocated around the high visual impact areas and in places where there are high frequency shadows.

melviso

Thanks for the link and info, mate.
High res lightmaps will be vital towards creating photorealism using ue4 to catch the global illumation, color bleed, bounced lighting and shadow details accurately. I am thinking using Texture atlas maps like this video would drastically reduce the draw call and improve performance for scenes rather than having elements with their own textures and materials. Thats where vertex painting using lerp and height lerp comes in.
You are right, I would have to try it out myself to determine the results.