Better transformation from EPSG:5683 to EPSG:3857

[ondrasvoboda]

I'm using ProjNET4GeoAPI to transform coordinates from EPSG:5683 to EPSG:3857, which works but the results are not so accurate. In QGIS I can see way better results with the following transformation pipeline:

Inverse of 3-degree Gauss-Kruger zone 3 + DB_REF to ETRS89 (1) + ETRS89 to WGS 84 (1) + Popular Visualisation Pseudo-Mercator
PROJ string:
+proj=pipeline
  +step +inv +proj=tmerc +lat_0=0 +lon_0=9 +k=1 +x_0=3500000 +y_0=0 +ellps=bessel
  +step +proj=push +v_3
  +step +proj=cart +ellps=bessel
  +step +proj=helmert +x=584.9636 +y=107.7175 +z=413.8067 +rx=-1.1155 +ry=-0.2824
        +rz=3.1384 +s=7.9922 +convention=coordinate_frame
  +step +inv +proj=cart +ellps=WGS84
  +step +proj=pop +v_3
  +step +proj=webmerc +lat_0=0 +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84

Can I somehow implement the same transformation also in ProjNET4GeoAPI?

[FObermaier]

If you need to use grid based transformation you could try (https://github.com/wo80/NTv2)

[ondrasvoboda]

I think grid transformation is not needed in this case. I need to implement DB_REF to ETRS89 (1) (https://epsg.io/5826) transformation step to make it work properly I think.

[oshawa-connection]

If you need to use grid based transformation you could try (https://github.com/wo80/NTv2)

Hi @FObermaier , I'm wondering would you accept PR's to add grid based datum transformations to this library using .tif + .gsb files?