[Qgis-user] Having trouble with prj-Files produced by QGIS

[Robert Nuske]

Hi

Shapefiles written with QGIS were not displayed correctly in other GIS and 
caused problems with ogr2ogr (reprojected points were shifted approximately 
180m).

Searching for a probable culprit I looked into different ways to reproject 
shapefiles, single coordinates and different prj-files. Finally comparing 
prj-Files produced by QGIS (Saving as... Shapefile or processing with fTools) 
with prj-files constructed by ogr2ogr and prj-files downloaded from 
spatialreference.org. Examples for two coordinate reference systems are 
attached, formatted to enhance the readability. 

Looking at those examples and some documentation on the web, I started to 
believe that the part --DATUM["D_unknown",-- in QGIS' prj-file could cause 
problems. In contrast to the first parameter/name of PROJCS and GEOGCS, the 
name of the DATUM seems to be a key that has to match an entry in a list of 
known datums and "D_unknown" was not found in that list.

Replacing QGIS' prj-file with prj-files of the same EPSG-Code from 
spatialreference.org led of course to a successful reprojection of the 
shapefile and correct placement of the points in various GIS.

Using QGIS 1.7 and gdal 1.8.0 form ubuntugis_unstable on Ubuntu 10.10.


So I am wondering: what did I do to mess up the prj-files so badly?
Any Hints? 


cheers,
  robert



PS: Is there any reason that the proj4-strings in QGIS (as shown in 
Settings/Project Properties/CRS) differ from the ones in PostGIS and 
spatialreference.org. QGIS seems to prefer +towgs84 instead of +datum.
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