[Proj] ToWGS84 for Germany, NRW?

[Jean-Claude REPETTO]

Bytechanger a écrit :
> Hi,
> 
> I want to convert 4326 to 31466....
> But there is a difference of 50m !!
> 
> I think I need right +towgs84 for Germany , NRW, Rhein-Erft-Kreis ??
> 

Hello,

PROJ.4 already contains the +towgs84 parameter :

cs2cs -v +init=epsg:31466
# ---- From Coordinate System ----
#Transverse Mercator
#	Cyl, Sph&Ell
# +init=epsg:31466 +proj=tmerc +lat_0=0 +lon_0=6 +k=1 +x_0=2500000 +y_0=0
# +ellps=bessel +datum=potsdam +units=m +no_defs +towgs84=606.0,23.0,413.0
#--- following specified but NOT used
# +ellps=bessel
# ---- To Coordinate System ----
#Lat/long (Geodetic alias)
#	
# +proj=latlong +datum=potsdam +ellps=bessel +towgs84=606.0,23.0,413.0

If it is not correct, you can find other ones in the EPSG database :
http://www.epsg-registry.org/

For my ttMaps software, I have used:
  +towgs84=598.1,73.7,418.2,0.202,0.045,-2.455,6.70


BTW, when you ask such a question, it is always better to give an 
example (input coords, output coords, expected coords).

Jean-Claude