I've decided that I would waste a lot less time finding good embarks with curious structures under them if I could see them on the embark screen. Finder doesn't point them out anymore, so I've been looking elsewhere. Legends doesn't seem to be helpful, nor does the xml dump. Zilpin's world tinker tool doesn't seem to export the locations of the structures either. I tried looking for identifiable strings that might be in world.sav or world.dat, but that didn't lead anywhere either. I then made a pocket world, found a structure, embarked there, and used dfliquids to make a few obsidian walls inside the structure, and then windiffed the save folders for the region and the backup copy I made just after embark. There were differences, but I wasn't able to find out which ones related to the demon fortress.
The file features 8-7.dat sounded like it might be useful, but I couldn't make sense of it. My last idea was to load it into xcel and try to make a histogram of the occurrence of each symbol in that file and see which ones exactly matched the number of region tiles on the map, and whether I could use that to construct an overlay for the detail map exported from legends mode.
Nothing but dead-ends yet.
From what I've seen, it seems that DFhack doesn't have anything that would extract the coordinates of fortresses either.
Does anyone know what, exactly, the underground regions section of legends does? The portion of the xml dump referring to that lists site ID, type (cavern, magma, or underworld) and depth (1,2,and 3 for caverns, 4 for magma, and 5 for underworld). There is never anything more specific than that. No coordinates, names, or anything.
Has anybody ever deciphered what the .dat files in the save directories do?