[Gdal-dev] ogr2ogr with reprojecting: DHDN to MGI Austria

[Frank Warmerdam]

Helmut Kudrnovsky wrote:
> my question: do i need also for the source an TOWGS84-parameter? if yes, do
> you have maybe a hint for me where i can find this?
> 
> -s_srs natura2000.prj
> 
> PROJCS["Germany_Zone_4", GEOGCS["GCS_Deutsches_Hauptdreiecksnetz", 
> DATUM["D_Deutsches_Hauptdreiecksnetz",

Helmut,

You need the TOWGS84 value for the source unless the source is very close
to WGS84 (as is the case with NAD83 for instance).

You may be able to find reasonable values in places like national mapping
agency web sites, or Cliff Mungier's past columns in the ASPRS magazine.
It may also exist in the original EPSG database (http://www.epsg.org).  In
many cases multiple TOWGS84 values exist in the EPSG database, and the
PROJ.4 translation includes none of them in order to avoid making an
arbitrary decision.

Good luck,

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