I don't understand why folks have to get these worlds so damn big. LOL
I was the same way so I understand that you don't understand what a large world is. Currently I have a world in BigWorlds engine that is 640 blocks x 512 blocks The hortizonal resolution is .7125 meters per division (was a major project to get the scale correct BTW). That is 81920 pixels x 65536 pixels. It takes over four hours to cross the world in the x direction. It is so unrealisticly big that for a commercial game it is probably not going to wash because it takes a whopping 56 giga bytes witht eh texturing masks.
After re-reading what you asked I believe this may be of use to you.
First off – Bigworlds has issues with large worlds so you need to mosaic the world off into different spaces. However, I work on one map to build the world and am writing a exporter for BWT that reads the world map and generates a mosaic spaces. The program is not complete at this writing because I decided to complete the other parts of the project and wait for the 2.1 release in case they change the terrain.
With that said – I wanted to get as close to realistic in size and scale that I could with L3DT and BWT. I selected the mid level detail of 128 pixels per 100 meters in BWT which is a .7125 meter per division. I created a 16 Giga-pixel design map at 1 meter per division so I could get some continental landmasses. Once I had a decent looking continent I selected it and saved it to a new layer. I resized this layer to a rough design of 1/8th the final map size (10240 x 8192) and the mosaic size of 1024. After generating the map at this size I then used the import design map function in L3DT and set the input read at 2 and output at 16 which makes a 8192 block at 1 meter per division. I had 64 tiles to process but they go a lot faster than L3DT because they are not mosaic.
With L3DT it is possible to generate a world size 16 time greater than 16 Giga-pixels using this method but the time involved and hard disk space required is beyond ones time or space.
Hope that helps ya..