[Proj] DHDN / Gauss Krueger to WGS84

[Mikael Rittri]

Hermann, 
you are right, of course.

In the original thread, DHDN zone 3 was mentioned,
but the discussion was mainly about the datum shift. 

Later in the thread, the test point was given, but without 
a zone number. (I suppose all German GIS people know that 
the leading digit of the Easting is the zone number.)

Thanks,

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com

-----Original Message-----
From: Hermann Peifer [mailto:peifer at gmx.eu] 
Sent: Friday, March 30, 2012 2:10 PM
To: PROJ.4 and general Projections Discussions
Cc: Mikael Rittri
Subject: Re: DHDN / Gauss Krueger to WGS84

On 30/03/2012 13:38, Mikael Rittri wrote:
> Hello Roger,
>
> Actually, I do believe that E 21.982946, N 48.433278 is the correct
> result, or at least more correct than E 11.446588, N 49.169494.
>
> Here is how I convinced myself...

Here is how I convinced myself that the opposite is true:

- DHDN = Deutsches_Hauptdreiecksnetz, a Datum used in Germany, i.e. not 
used at E 21.982946
- in a coordinate system based on 3-degree zones, it doesn't make much 
sense to have x-values which are 959750 m east of any central meridian
- at school, I learned: if the leading digit of the x-value is 4, than 
you are in 3-degree Gauss-Kruger zone 4 (nowadays also known as epsg:31468)
- GK3 zone 4 has a central meridian of 12 degrees East and a false 
easting of 4500000m, see also [1]

Given the above, you end up with:

echo "4459750 5448182" | cs2cs -f "%.6f" +init=epsg:31468 +to 
+init=epsg:4326
11.446584       49.169489 50.081973

(i.e. some 100+ km north of Munich)

Hermann

[1] 
http://upload.wikimedia.org/wikipedia/de/1/12/Gau%C3%9F-Kr%C3%BCger-Raster_Deutschland.png