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

[Tobias Wendorff]

Am 08.03.2011 14:53, schrieb Josh Doe:
> And as far as OSM putting "both datums on the same level", I have to
> disagree. OSM itself explicitly says all coordinates are in WGS84.
> There may be certain applications which mix things up, but that's not
> the fault of OSM.

Let me explain it in numbers, perhaps my English is too bad:

WGS84 coordinates (LAT,LON): 51.0, 7.0
[1] projection to EPSG:3785 (x,y): 5677294.03, 781182.21 (sphere)
[2] projection to EPSG:3857 (x,y): 5677294.03, 775978.50 (ellipsoid)

When a software uses the spherical formular of mercator, the
coordinates will be drawn at "5677294.03, 781182.21".

If the inverse mercator formular is also the spherical one,
more errors will be added... x/y-coords to geographical ones:
[3] 5677294.03, 781182.21 => 51.000000, 7.046703

Used parameters on cs2cs:
[1] cs2cs +proj=latlong +datum=WGS84 +to +proj=merc +a=6378137 \
+b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m \
+nadgrids=@null +no_defs

[2] cs2cs +proj=latlong +datum=WGS84 +to +proj=merc +datum=WGS84 \
+units=m +nadgrids=@null +no_defs

[3]
cs2cs +proj=merc +datum=WGS84 +units=m +nadgrids=@null +no_defs \
+to +proj=latlong +datum=WGS84 -f %.6f