[PROJ] EPSG:4326 --> EPSG:5677

[Javier Jimenez Shaw]

Hi Roger

For the vertical heights you can use EPSG:7837 "DHHN2016 height"
So maybe you can go from EPSG:4937 (ETRS89 3D) to EPSG:5677+7837 (compound)

About DHDN and other German datums, there is a talk from FOSSGIS 2025 (in
German):
https://www.youtube.com/watch?v=-7PpQMHoOFM

On Wed, 24 Sept 2025 at 12:03, Even Rouault via PROJ <proj at lists.osgeo.org>
wrote:

> Roger, (sorry for the first name error in my previous email)
>
>
>
> I see that three possible operations are listed. To be honest, I do not
> know which one is most appropriate.
>
> No worry. You're not alone. It depends on the context...
>
> I am guessing that #1 is the default.
>
> The grid based has the best accuracy, so when the grid is available, it is
> indeed used
>
> How would I choose one of the other sets of operations? Use the listed
> strings as the destination CRS? Or is there some other way to select it?
> Should the reported altitude always be over the new ellipsoid?
>
> If you want 3D operations, you should use the 3D versions of the CRS. You
> can add the --3d flag to projinfo to force promotion. But in the case of
> DHDN there's no official 3D version of the CRS in the EPSG dataset, so what
> PROJ will report may be dubious.
>
> If you try "projinfo EPSG:4326 EPSG:5677 --spatial-test intersects
> --grid-check none  --3d --single-line -o PROJ", the second operation will
> be:
>
> +proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert
> +xy_in=deg +z_in=m +xy_out=rad +z_out=m +step +proj=cart +ellps=WGS84 +step
> +inv +proj=helmert +x=598.1 +y=73.7 +z=418.2 +rx=0.202 +ry=0.045 +rz=-2.455
> +s=6.7 +convention=position_vector +step +inv +proj=cart +ellps=bessel
> +step +proj=tmerc +lat_0=0 +lon_0=9 +k=1 +x_0=3500000 +y_0=0 +ellps=bessel
>
> And you can create a PJ object from it with
>
> myTransf = proj_create(ctxt, "+proj=pipeline +step +proj=axisswap
> +order=2,1 +step +proj=unitconvert +xy_in=deg +z_in=m +xy_out=rad +z_out=m
> +step +proj=cart +ellps=WGS84 +step +inv +proj=helmert +x=598.1 +y=73.7
> +z=418.2 +rx=0.202 +ry=0.045 +rz=-2.455 +s=6.7 +convention=position_vector
> +step +inv +proj=cart +ellps=bessel +step +proj=tmerc +lat_0=0 +lon_0=9
> +k=1 +x_0=3500000 +y_0=0 +ellps=bessel")
>
>
>
>>
>>
>>
>> Even
>> Le 24/09/2025 à 08:57, Roger Oberholtzer via PROJ a écrit :
>>
>>
>>
>> I am trying to project some EPSG:4326 locations (from a GPS) to
>> EPSG:5677 (DHDN Germany Zone 3). I have sample data from the German road
>> authorities (BASt). They feel that the locations provided by proj (9.6.0)
>> are consistently 1.5 meters or so away from that they expect. They were
>> also expecting a change in altitude as the ellipsoid was different. I have
>> implemented this with something like this:
>>
>> myCRS = proj_create_crs_to_crs( 0,  "EPSG:4326",  "EPSG:5677",  0);
>>
>> And then calling proj_trans(myCRS, PJ_FWD, PJ_COORD);
>>
>> My question is if I need to do more than this as EPSG:5677 is ellipsoid
>> Bessel 1841.
>>
>> --
>> Roger Oberholtzer
>>
>> _______________________________________________
>> PROJ mailing listPROJ at lists.osgeo.orghttps://lists.osgeo.org/mailman/listinfo/proj
>>
>> -- http://www.spatialys.com
>> My software is free, but my time generally not.
>>
>>
>
> --
> Roger Oberholtzer
>
> -- http://www.spatialys.com
> My software is free, but my time generally not.
>
> _______________________________________________
> PROJ mailing list
> PROJ at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/proj
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/proj/attachments/20250924/98698d97/attachment.htm>