I have to transform Gauss Kruger coordinates to Long/Lat coordinates in WGS84 and ETRS89. I have really no knowledge about all these coordinate systems and their transformations. My background is just software engineering. I just have to do this, because our system only supports Long/Lat coordinates in WGS84 and ETRS89, but a few sub systems deliver only Gauss Kruger coordinates, so I need to transform them. I have to integrate the transformation in a Java application.

I made some research on my own an I tried using the Java library of PROJ.4, but I do not get accurate results.

I used it as follows:

proj +proj=tmerc +lat_0=0 +lon_0=6 +k=1 +x_0=2500000 +y_0=0 +ellps=bessel +datum=potsdam +units=m +no_defs

For example, for

N: 5705784, E: 2944378

I get

Long: 12.377177, Lat: 51.314087

But the result should be:

Long: 12.375598, Lat: 51.312832

Is this difference normal?

How can I get more accurate results?

Other libraries are also fine.