[Tilesathome] Tileset as one file v2

[spaetz]

I just read through the tileset as one file v2 description on the wiki. A couple of comments:

- Looks ok in general

* ''userid'' is set twice, once in the beginning of the file and once as "metadata" in the end. Do we really need to set it twice? I'd rather not.

- we have the base zoom level at the end and the number of zoom levels and the first zoom level in the beginning of the file. Is this inconsistency needed? Why not put the base zoom level in the last byte at the beginning of the file too?
- Also, I am still a bit sceptical about that "size" data. It does mean that the tile serving module needs to do more work for each served tile even if t@ is never going to need it. Why can't we just skip this and those who want to skip levels just leave them as "0" (unknown) tile in their tileset files (e.g. this means 5*4 bytes wasted, if mapnik people want to start a tileset at z14 (containing 4x4 tiles)).

- OSM-Timestamp can be easily be shown via tilesetfile mtime, for example. So while I don't mind this as metadata, it does blow up our disk usage (although it's unclear whether the time stamp is recorded as a string or as a binary number). This should be clarified at least.

- Is this true?
"Therefore, the offset to the last index entry (which is pointing to the start of meta data) is: 8 + 4 * ni"

This would result for a regular z12 tileset in:
8 + 4 * ((pow(4,6)-1)/3) =5468
As we have 1 more index entry as tiles, this should be 8 + 4 * (ni+1) in my opinion. Right, or have the pain killers dimmed my mind?

- Generally it remains unclear how "tile, x,y,zoom" info is stored as metadata, string or binary number? Also for layer, do we store "captionless" in each tileset file, or the server internal layer number?

Overall, I am fine with the changes. I will be looking into a way to store the tileset file at it's final place as part of the upload process, so that we can ditch the serparate upload processor again, if possible.

spaetz