Setting up Lightmaps can be cumberstone, but it is not impossible though.
I suggest some form of automation during the Datasmith import process could be handy: basically automatically enable lightmaps for each imported mesh (“Generate Lightmap UV” setting), and scaling lightmap resolution according to the size of the mesh (“Min Lightmap Resolution” setting).
I think it is feasible to automate this step with some custom import pipeline.
Once this have been automated, then the rest should just to manually build the lightmap (which could take a lot of processing time indeed).
Start small:
- Have a sample 3DSMax scene, with a few objects of various sizes
- For each mesh, adjust the mesh settings to generate lightmaps correctly
- Generate the lightmap, and see what happens
- Tweak the settings until you find what’s right for your typical objects
- Once you found the best settings, try to automate this in a custom import pipepline (if this is feasible)
Good luck !
Hint: the “Lightmap density” view mode might help you to find the best lightmap resolutions according to the object sizes