Feature request #11347
Unneccessarily inaccurate transformation Gauß-Krüger to UTM
|Pull Request or Patch supplied:||No||Resolution:||up/downstream|
|Easy fix?:||No||Copied to github as #:||19638|
Some months ago I reported what I believed to be a bug in transforming East German Krassovski coordinates to other projections like UTM. I was tought that due to limitations in Proj.4 there is only one transformation for each EPSG code, so there is no choice of transformation. Compared to ArcGIS that's a serious disadvantage. It can easily be overcome by the knowable, in case of the east German transformation you just have to edit the +towgs part (change to +towgs84=24,-123,-94,0.02,-0.25,-0.13,1.1).
However I doubt that it makes sense to get users into trouble like that if it can easily be prevented. There is a long-standing precise official transformation for Gauß-Krüger (Bessel) to UTM in Germany called Beta2007, but for reasons I don't (want to) understand it's not delivered with the QGIS package so far. We are in Germany in the middle of a process switching from Gauß-Krüger to UTM. But every time users use QGIS to reproject data they introduce shifts of up to 3 meters (indeed quite exactly 3 meters in the southwest of Germany). For my part, I can't use QGIS if I have to be afraid that the data I deliver have to be considered as faulty, if I (or others) need sub-meter precision.Meanwhile I found the solution, which should be delivered as default:
- Download BETA2007.gsb, official site: http://crs.bkg.bund.de/crseu/crs/descrtrans/BeTA/BETA2007.gsb
- Save it to the <QGIS program path>\\share\\proj
- Add custom CRSs (On the long run they should replace the existing EPSG declarations):
Name: GK2 DHDN / Bessel (Beta2007) EPSG 31466 Parameter: +proj=tmerc +lat_0=0 +lon_0=6 +k=1 +x_0=2500000 +y_0=0 +ellps=bessel +units=m +nadgrids=BETA2007.gsb +no_defs Name: GK3 DHDN / Bessel (Beta2007) EPSG 31467 Parameter: +proj=tmerc +lat_0=0 +lon_0=9 +k=1 +x_0=3500000 +y_0=0 +ellps=bessel +units=m +nadgrids=BETA2007.gsb +no_defs Name: GK3 DHDN / Bessel (Beta2007) EPSG 31468 Parameter: +proj=tmerc +lat_0=0 +lon_0=12 +k=1 +x_0=4500000 +y_0=0 +ellps=bessel +units=m +nadgrids=BETA2007.gsb +no_defs
I think QGIS is a great achievement, and I'm grateful to everybody who takes part in the concerted efforts of developing it. It would be a pity if its usefulness is severly limited by such an issue.