[Tilesathome] t at h omsa / mapnik / storage clarification

[Sebastian Spaeth]

Life Tester wrote:
> q1. is t at h dedicated only to osmarender?

T at h currently only uses osmarender. Although the server doesn't care how
the resulting tiles are being created. The server sends out render
requests for some layer to the clients and the clients upload some image
files. So all the logic which renderer is being used is in the clients.


> q2. what is the purpose for mapnik render? does it cover the same zoom
> levels as osmarender?

Mapnik is a cool rendering mechanism that is being used for the main
layer on the openstreetmap.org website. Both (t at h and mapnik) use osm
data, but that is where the relationship ends. They are totally
different systems.

> (I'm trying to figure out how come one is using the power of the peers
> and the other one seems not)

One of them distributes the rendering load on the peers, while the other
relies on a central local database that it uses. Mapnik is much more
efficient in the design so it manages to render all tiles on just one
machine just fine (as long as you have an up to date osm database).

>>> 20:51 < spaetz> http://tah.openstreetmap.org/media/filesizes.bz2
>>> 20:52 < spaetz> result of ls --file-type -l -R > filesizes
>>> 20:52 < spaetz> takes some grepping, and cutting to get the raw sizes,
> 
> and (I did) a bit of math:  ~1M objects, ~600GB
> 
> q3. would it be possible to run the same for the other zoom levels?
> (just curious how much data are you looking at)

Those files sizes include z12 to z17, so they cover the most relevant
zoom levels.
The z6-11 tileset files are all around 4MB per piece. While empty tiles
in z12-17 do not exist as tileset files, those low zoom files will exist
even if just empty blue.

> q4. in the wiki (old page maybe?) there was a call for dedicated
> servers. what specs are you/OSM looking for? (if the request is still
> valid)
I got ETH Zurich to donate a server and bandwidth to keep t at h running,
and for that setup it seems sufficient. The server has not enough RAM to
run a mapnike/postgis installation but for doing what it currently does,
it seems pretty good. The most severe bottleneck by far is development
man power.

> q5. there was a thread/project about aerial imagery and (free)
> sources. is this project still live? what would be show stoppers here?
> (except maybe for someone to drive it :-)

Chris Schmidt ran that project. But afaik the disk requirements were
above everything that could be organized/managed. Plus, someone to drive
it. Obviously. (plus, some unresolved licensing issues, if I remember
correctly).
openairialmap would probably best be set up as an independent
project..., I guess. (I am not affiliated with the OSM foundation, so
take my opinion with a grain of salt).

spaetz

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