[OSM-dev] Kosmos != Mapnik, Osmarender - projection problem

[Dirk-Lüder Kreie]

Igor Brejc schrieb:
> Hi all,
> 
> I've added slippymap-like rendering directly into Kosmos GUI (it will be 
> available in the next version, probably within a week). Anyway, I've 
> noticed that there is an discrepancy between Kosmos rendering and tiles 
> generated by Mapnik (and Osmarender). All the stuff Kosmos renders is 
> offset slightly towards the north (or south, depending on the 
> hemisphere). 

> I've double-checked my math and cannot find what could be wrong. I'm 
> assuming that Mapnik and Osmarender use spherical Mercator projection 
> (and not elliptical). Possible explanations:
> 1. My projection math is wrong
> 2. There is a difference between .NET math calculation and that of 
> Mapnik's C++
> 3. I use double precision, while others use plain float?
> 4. ...?
What do you use to calculate the maxX (trivial) and maxY coordinates for 
the tiles?
There might be a hidden rounding error.

All projection code used for tiles at home is in svn:
http://svn.openstreetmap.org/applications/rendering/tilesAtHome/lib/tahproject.pm

> Any help would be appreciated.


-- 

Dirk-Lüder "Deelkar" Kreie
Bremen - 53.0952°N 8.8652°E