[josm-dev] projection Mercator, set EPSG 3785 instead of EPSG 3857

[M∡rtin Koppenhoefer]

2011/2/25 Josh Doe <josh at joshdoe.com>:
> Hmm, but EPSG:3785 is deprecated, or as EPSG says, "NOT VALID".
> EPSG:3857 is equivalent to EPSG:3785, it's just a different
> formulation. Here's the change request from EPSG's site (notice the
> Actions Take section):

I know that EPSG says "NOT VALID". Who cares?

If you look at the specs they are not equivalent (inverse flattening +
ellipsoid vs. sphere). When I created my hillshading I first used 3857
(assuming it was 900913) and it didn't fit with the
OSM-Mapnik-Rendering. There was a slight offset that disappeared when
I reprojected them in Grass GIS to 3785. I tried this empirically and
it worked. They cannot be the same (or the Proj.4 has/had a bug).

I also asked on the mapnik mailing list and they confirmed that we are
not using the inverse flattening (i.e. 3857). I am aware that the web
is full of people stating that these 2 are the same.

Cheers,
Martin