[OSM-dev] mod_tile in other projections? (2018)

[Christoph Hormann]

On Friday 26 October 2018, Eduardo Ramalho wrote:
>
> Now I am trying to only show a country (Portugal)
> with its specific projection EPSG:3763.
>
> I changed the "mapnik.xml" to have my target "srs" and specific
> cartesian bounds, also changed renderd.conf to have aspectx=1 and
> aspecty=2,
> and finally removed all cached tiles.
>
> When I check the request url for /0/0/0.png I get a world view bitmap
> (but very distorced).
> I was expecting to get only the half north of Portugal on zoom level
> 0.

Something like this is to be expected.

Mapnik supports rendering in arbitrary projections but renderd and 
mod_tile are likely hardcoded to Mercator and what you probably get is 
your local coordinate system but rendered with the mercator bounds - 
which of course does not make any sense.

For local coordinate systems there is no natural tile system so what 
tile 0/0/0 shows exactly depends on the projection *and* the configured 
bounds.  The bounds you define in mapnik are just the limits of the 
area mapnik renders.  But mapnik does not know anything about tiling, 
this is done by renderd.

The funny thing is that the tile manager could be completely projection 
agnostic, it would not even need to know what projection the map is in, 
it would just need to know the bounds of tile 0/0/0 in the desired 
projection - and divide these bounds as needed to generate the 
rendering requests for mapnik.

-- 
Christoph Hormann
http://www.imagico.de/