DB_REF is the official reference system for german federal railways - Deutsche Bahn (DB). For a description, see here: http://download-data.deutschebahn.com/static/datasets/aufzug/DB_REF.pdf (german)

The document mentions several EPSG codes, see below. However, trying to view any coordinates given in DB_REF (the actual EPSG code is missing very often), i come up with a position offset of 100m - 500m:

enter image description here

This is elevator dataset (http://data.deutschebahn.com/dataset/data-aufzug) in DB_REF assumed CRS is EPSG:5683, compared with OSM tiles and railway line network (http://data.deutschebahn.com/dataset/geo-strecke), provided in EPSG:4326 (map projected to EPSG:3857). Elevators should be placed on the platforms, between the lines.

Same offset issue occurs when I attempt to save my own data in DB_REF using QGIS - they get an offset to external DB_REF data.

Am I missing any DB_REF CRS? Or could the DB_REF definitions used by QGIS be wrong?

EPSG codes:

  • 1081 Deutsche Bahn Reference System
  • 5825 DB_REF geocentic
  • 5826 DB_REF to ETRS89
  • 5681 DB_REF geografic 2D
  • 5830 DB_REF geografic 3D
  • DB_REF / 3-degree Gauß-Krüger
    • 5682 zone 2 (E-N)
    • 5683 zone 3 (E-N)
    • 5684 zone 4 (E-N)
    • 5685 zone 5 (E-N)
  • DB_REF / 3-degree Gauß-Krüger+DHHN92 height
    • 5832 zone 2 (E-N)
    • 5833 zone 3 (E-N)
    • 5834 zone 4 (E-N)
    • 5835 zone 5 (E-N)

The DB_REF definitions in QGIS are wrong (at least in QGIS2).

They are missing any +towgs84 parameter, which is necessary for the DHDN datum.

Instead of EPSG:5683, take EPSG:31467 which has the correct datum shift values.

The linked document lists datum shift values that differ from EPSG:31467, so you might use these PROJ strings instead:

For GK2:

+proj=tmerc +lat_0=0 +lon_0=6 +k=1 +x_0=2500000 +y_0=0 +ellps=bessel +towgs84=584.9636,107.7175,413.8067,1.1155214628,0.2824339890,-3.1384490633,7.992235 +units=m +no_defs

For GK3:

+proj=tmerc +lat_0=0 +lon_0=9 +k=1 +x_0=3500000 +y_0=0 +ellps=bessel +towgs84=584.9636,107.7175,413.8067,1.1155214628,0.2824339890,-3.1384490633,7.992235 +units=m +no_defs

For GK4:

+proj=tmerc +lat_0=0 +lon_0=12 +k=1 +x_0=4500000 +y_0=0 +ellps=bessel +towgs84=584.9636,107.7175,413.8067,1.1155214628,0.2824339890,-3.1384490633,7.992235 +units=m +no_defs

Comparing with datum transformations with BETA2007 and EPSG:31466, DB_REF is about half way between them. BETA2007 is 1.2 meters away, ESPG:31466 0.5 meters.

  • That seems to work, but how can I be sure it's truly accurate? I get no official information on DB_REF except for the document cited above. The wrong definition of DB_REF is widely spread, covering QGIS 3, epsg.io (epsg.io/5683) and other EPSG registries. – fuzzysolutions Oct 24 '18 at 9:56
  • 1
    You find the correct datum shift in the document you linked under (4). – AndreJ Oct 24 '18 at 12:26
  • So this contains alle the information I need to build my own proj4string for a custom CRS definition in QGIS? Great. I'll dig into it and try. I have to shelve the topic a little bit, but I'll come back with my results. – fuzzysolutions Oct 30 '18 at 11:17
  • 1
    Related: github.com/OSGeo/proj.4/issues/1167 – AndreJ Oct 31 '18 at 16:31

Solved in PROJ master (https://github.com/OSGeo/proj.4/issues/1167) - correct DB_REF will be available to QGIS users after PROJ version 6.0 is rolled out on 2019/02 (- or by building PROJ-master and GDAL from source).

Thanks to AndreJ for the issue on PROJ and his remarks to my post.

  • But only with current PROJ master, or not? – AndreJ Dec 13 '18 at 7:14
  • Yes, and PROJ master is being installed with current QGIS installations / updates, right? – fuzzysolutions Dec 13 '18 at 9:10
  • No, current builds come with the latest PROJ release version 5.2. Master is the base for the next release version 6.0. And it needs a new GDAL release version as well. Until then, you have to compile PROJ and GDAL from master sources yourself to get the changes. – AndreJ Dec 13 '18 at 9:33
  • See my edit of my answer. – fuzzysolutions Dec 13 '18 at 9:53
  • If you type gdalsrsinfo EPSG:5683 inside the OSGEO4W shell, do you get datum shift parameters? – AndreJ Dec 13 '18 at 14:14

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