[Qgis-user] How to fix a CRS definition?

[Andre Joost]

Am 23.12.2012 12:32, schrieb Anita Graser:
> Hi,
>
> In my QGIS 1.8 install on Ubuntu EPSG:31287 is defined as
>
> +proj=lcc +lat_1=49 +lat_2=46 +lat_0=47.5 +lon_0=13.33333333333333
> +x_0=400000 +y_0=400000 +ellps=bessel +datum=hermannskogel +units=m
> +no_defs
>
> while according to http://spatialreference.org/ref/epsg/31287/proj4/
> (and the definition used in PostGIS) it should be
>
> +proj=lcc +lat_1=49 +lat_2=46 +lat_0=47.5 +lon_0=13.33333333333333
> +x_0=400000 +y_0=400000 +ellps=bessel
> +towgs84=577.326,90.129,463.919,5.137,1.474,5.297,2.4232 +units=m
> +no_defs
>
> Has this been fixed in Master? Is it possible to change this for 1.8
> on my machine? It seems to cause an east-west offset.

The '+datum=hermannskogel' is hardcoded in proj:
<https://svn.osgeo.org/metacrs/proj/branches/4.8/proj/src/pj_datums.c>
with a three-parameter transformation:
"hermannskogel", "towgs84=653.0,-212.0,449.0"

Seven-parameter transformations are more precise, the official 
parameters can be found here:
<http://mapref.org/GeodeticReferenceSystemsAT.html>

The latest build of gdal uses the 7 parameters you listed above.

If you want to change the values, look for srs.db. You can edit it with 
spatialite, or just copy it from the windows installations.

Greetings
André Joost