Now i have a big level but only a small part of it is textured and has foliage and stuff on it. probably 10% of the actual map size. now how can i build only the lighting and everything for this small area? i have the lightmass volume as small as i can get it with still covering all of my assets. i heard about a thing called world composition but out of the documentation i have no idea how to use it. is there any other way? otherwise building the lighting just takes forever, and i have a pretty beefy PC wich should be able to handle it quite easy
Having the beefy PC is not enough, while you are working with large spaces and high lightmap resolutions. It is not like magic, and you need a lot of CPU power with many cores, to improve the building speed, and newest i7 is not the finest CPU for this things, so it have to take some time.
I don’t know how to build only part of scene and I do believe that it is not possible, but there is walk-through if you want to tweak some parts of the scene, without waiting years.
Just select the part of the scene that is important for you, migrate it to the new level or new project, and then do tweaks on this new project. When you will be happy with the result, you can remigrate it back to the project, or just know what you need to do in the final scene.
My technique is to move all objects to “movable” and set only the objects that I want to bake in static