[gdal-dev] ogr2ogr and +towgs84

[Frank Warmerdam]

Armin Burger wrote:
> Hi everybody
> 
> I need to convert a shapefile in a UTM projection with datum ED50 to a 
> WGS84 based projection (LAEA, Epsg 3035). I applied the datum shift 
> parameters using "+towgs84", like
> 
> ogr2ogr -f "ESRI Shapefile" -s_srs "+proj=utm +zone=30 +ellps=intl 
> +units=m +towgs84=-131.0,-100.3,-163.4,-1.244,-0.020,-1.144,9.39 
> +no_defs"  -t_srs "EPSG:3035"  with_datumshift test.shp
> 
> but it seems whatever I write for +towgs84 has no effect. I can drop it 
> completely or use other values, the result is always the same. Is the 
> +towgs84 parameter just not used or do I use a wrong definition somewhere?
> 
> GDAL version used is the one from FWTools 2.1.0 (Win)

Armin,

EPSG:3035 translates as:


PROJCS["ETRS89 / ETRS-LAEA",
     GEOGCS["ETRS89",
         DATUM["European_Terrestrial_Reference_System_1989",
             SPHEROID["GRS 1980",6378137,298.257222101,
                 AUTHORITY["EPSG","7019"]],
             AUTHORITY["EPSG","6258"]],
         PRIMEM["Greenwich",0,
             AUTHORITY["EPSG","8901"]],
         UNIT["degree",0.01745329251994328,
             AUTHORITY["EPSG","9122"]],
         AUTHORITY["EPSG","4258"]],
     UNIT["metre",1,
         AUTHORITY["EPSG","9001"]],
     PROJECTION["Lambert_Azimuthal_Equal_Area"],
     PARAMETER["latitude_of_center",52],
     PARAMETER["longitude_of_center",10],
     PARAMETER["false_easting",4321000],
     PARAMETER["false_northing",3210000],
     AUTHORITY["EPSG","3035"],
     AXIS["X",EAST],
     AXIS["Y",NORTH]]

or in PROJ.4 :

  +proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 
+units=m +no_defs

So the problem is that it does not have any datum shift info, and so datum
shifting is disabled in PROJ.4.

If you want to treat EPSG:3035 as being on a WGS84 datum try using:

  -t_srs '+proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +datum=WGS84'

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org