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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.

  • Is your source system this one spatialreference.org/ref/epsg/31466? What is your reference for getting the correct result? – user30184 Mar 1 '17 at 11:24
  • Unfortunately, I don't know what zone the source system uses. It is now our system. I just know they are using the Bessel ellipsoid. Is that not enough? – Javiator Mar 1 '17 at 11:27
  • You're missing the geogrpahic/datum transformation parameters to convert from whatever datum the GK zone is on ("Potsdam"?). It may be DHDN based on a CM of 6. There are 3 possibilities in EPSG registry depending on location in Germany. They also may not be the same values being used by Proj.4 but should be closer. – mkennedy Mar 1 '17 at 20:53
  • Exactly. I also found that out earlier today. I am using EPSG:31466 (GK zone 2) now and I getting really close. I just have a deviation of about 4 meters. Can I get even closer? – Javiator Mar 1 '17 at 21:01
  • How do you know that the "correct" result is 12.375598/51.312832? The tool (or person or document) should be able to provide more detailed information about which values are used. – Wernfried Domscheit Mar 23 '17 at 13:49
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With GDAL 2.2-dev I get results which are closer to those that you consider correct. The Proj.4 version in that build is proj-4.8.

gdaltransform -s_srs epsg:31466 -t_srs epsg:4326
2944378 5705784
12.3756178459526 51.3128099490148 44.7304746098816

I suggest you to check which version your library is and update if it is older as the first step.

You should also find out what is your reference implementation so that others can evaluate if that is something that is known to be good for your area (Germany?).

  • I did not understand you last sentence. What do you mean with reference implementation? The source system? – Javiator Mar 1 '17 at 11:51
  • With the reference implementation I mean the program/algorithm/method that you are using when you convert N: 5705784, E: 2944378 and get result Long: 12.375598, Lat: 51.312832. You are using that as a reference when you say that Long: 12.377177, Lat: 51.314087is not accurate. – user30184 Mar 1 '17 at 13:15

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