The global scenery comes in two packages in version 9: -global terrain- and -global overlays-. The global terrain package contains the base meshes (with beaches); the global overlays contain roads, forests and objects.
Why is this scenery split in half? The answer is unfortunately not “so you can replace the base mesh but keep the overlay 3-d stuff.” That would have been clever, but I must admit I didn’t think of it at the time; MeshTool didn’t exist and people just weren’t making base meshes.
My actual goal was to make it cheaper to replace a significant number of overlays. I don’t know if we’ll ever do this, but one of the obstacles to patching global scenery is the file size; we can only hope to replace a fraction of the files during a version run before the web update size gets too large. But most of that size is in the base mesh. With the base mesh and overlay split, we could potentially replace more overlays.
(Note: we did not actually issue any DSF replacements during the v8 run, and I don’t know if we will or will not during the v9 run. The only thing I am sure of is that if we provide replacement v9 DSF tiles, they’ll be a free download, like all v9 patches…if you buy v9, you get everything.)
The fundamental problem with replacing the base mesh but not the overlays is that the scenery system provides no good way to do this. The Global Scenery folder is always scanned after the Custom Scenery folder* so you’d have to install custom scenery into the global scenery folder with the right file name to get access to the overlay content.
I’m not sure what to do about this yet; the trend in scenery development is for authors to want more control to replace individual parts of the system; the overlay system provided part of that.
* Users with v9 beta DVDs will have the two global scenery folders in the Custom Scenery folder. But — the sim detects this and simply treats them as if they were in the Global Scenery folder, ignoring alphabetic ordering.
