Am 22.03.12 09:28, schrieb bernhard.stro...@jena.de:
Problem confirmed here
Example of prj file (produced by GRASS):
PROJCS["Transverse_Mercator",GEOGCS["GCS_bessel",DATUM["D_Deutsches_Hauptdreiecksnetz",SPHEROID["Bessel_1841",6377397.155,299.1528128]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",12],PARAMETER["scale_factor",1],PARAMETER["false_easting",4500000],PARAMETER["false_northing",0],UNIT["Meter",1]]
QGIS loads this with EPSG:2167 which contains the following proj4
parameters:
+proj=tmerc +lat_0=0 +lon_0=12 +k=1 +x_0=4500000 +y_0=0 +ellps=krass
+towgs84=26,-121,-78,0,0,0,0 +units=m +no_defs
whereas EPSG:31468 has:
+proj=tmerc +lat_0=0 +lon_0=12 +k=1 +x_0=4500000 +y_0=0 +ellps=bessel
+towgs84=582,105,414,1.04,0.35,-3.08,8.3 +units=m +no_defs
The problem may be there are no explicit towgs84 parameters BUT there is
a datum given in the prj file which other software translates into a
towgs84 parameter and vice versa, QGIS does not.
... and Qgis has picked another ellipsoid (Krassowsky instead of Bessel,
which is definitely wrong.
I had similiar problems when transformning Geotiff raster data from DHDN
to Google Mercator using gdalwarp: EPSG:900913 always gave an offset to
the north by 20km, while using EPSG:3785 was placed correctly.
By the way, the towgs84 paramters for DHDN are only a rough geuss. Exact
values differ from region to region, or can be replaced by the
high-accuracy beta2007 transformation.
Greetings,
Andre Joost
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