[OSM-dev] mod_tile in other projections?

[Kai Krueger]

On 03/07/2013 08:36 AM, Jason Lee wrote:
> Hi all,
> It might seem an odd question but I'll give it a shot - would 
> mod_tile/renderd support the dynamic generation of map tiles in a map 
> projection other than web mercator? If not, then would it be 
> possible/how difficult would it be to modify the code to support it?
If by dynamic you mean you want to be able to select a different 
projection on every request, then that is currently not possible. 
However I am working on making mod_tile more configurable / 
paramerizable which can possibly be used for different projections per 
request as well. It is initially intended to make seting up rendering of 
multi-lingual maps like [1] easier, but it is basically just an 
extension to be able to pass in an arbitrary string parameter to renderd 
that can then parameterize the mapnik map object in various ways.  With 
this you could have URLs like http://yourtileserver.org/tiles/srs 
27700/0/0/0.png using mod_tile and renderd.

If you mean dynamic generation of tiles that are always in the same 
projection albeit a different one than web mercator, then that should 
probably be doable with little modifications. The main issue I see with 
that is the tile numbering schema. I presume not all projections have 
the same numbering schema of (z^2) x (z^2) tiles per zoom level. At the 
moment there are a number of sanity checks in mod_tile and renderd that 
filter out requests that don't adhere to this restriction. However, it 
should be fairly trivial to modify those checks to reference the 
appropriate checks for the projection you wish.  There are a few other 
minor modifications you would likely need in renderd, but from a quick 
glance over the code, they should be rather easily doable.

Kai
>
> The only other thing I can think of is using MapProxy with Mapnik 
> backend but I'm not sure the scalabilty/performance compared to mod_tile.
>
> Thanks and regards,
> Jason

[1] http://mlm.jochentopf.com/