@nus I meant to implement roaring maps but never ended up doing so (burned out etc.)

They do some combination of storing bits as-is, or switching to run length buckets, depending on the actual patterns of bits and some heuristics, so large solid surfaces or empty surfaces would actually just be stored in a tree that says "voxel 0-4000 are empty"

I don't know that they do this. It could just be lz4 or something basic.