[Tilesathome] Tileset files

Matthias Julius lists at julius-net.net
Tue Sep 16 13:47:49 BST 2008


spaetz <osm at sspaeth.de> writes:

> On Tue, Sep 16, 2008 at 10:33:09AM +0200, Dirk-L?der Kreie wrote:
>> would it overcomplicate things to put some metadata into a tileset
>> file, so the client can record information about the rendering
>> process (which datasource, which osmarender, which rasterizer and so
>> forth)?
>
> Well, you have those tilesets about 16 mio time per layer. since the
> tileset format works with fixed offsets you'd have to reserve 100
> bytes for a renderer name, 8 bytes for the x,y, a byte for the layer
> etc.
>
> Is this really worth the bloat? We know who uploaded a tileset and we
> know when it was rendererd.

How do you know when it was rendered?  Does the server look at the
file dates of the PNG files?

It would be more important to know when the OSM data was downloaded.

>
> I am not opposing it. Someone just needs to adapt all the tools that
> work with it (mod_tah.c, server, client) to allow for that and allow
> for a gradual switchover too. Can it be done? yes. Does it require
> effort and will destabilize things even more for a time? likely.

I was proposing to put that data at the end of the file.  So, the last
offset in the index would point to the start of the meta data instead
of the end of the file.  This way current tools will just ignore it
and it is easy to find for tools that are aware of it.  They just need
to read from the last offset to EOF.

>
>> And since you have to take care of endianness, what's with older
>> macs?
>
> Endianness is defined as described in tileset-as-one-file in the wiki.

Perl should take care of making sure everything is little endian.  The
client uses pack("V*") to write the offsets.

Matthias




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