[gdal-dev] Datum transformation method when projecting from a sphere to NAD83 shapefile

Frank Warmerdam warmerdam at pobox.com
Tue Sep 9 14:57:07 EDT 2008

Limei Ran wrote:
> Hi Frank:
> You mentioned that I have not provided a datum definition for the source 
> coordinate system, only an ellipsoid definition.   Could you tell me how 
> I can provide the datum definition to get the same result from PROJ4.5?
> The command I used is:
> ogr2ogr -t_srs "+proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=23 +lon_0=-96 
> +x_0=0 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs " -s_srs 
> "+proj=lcc +a=6370000.0 +b=6370000.0 +lat_1=33 +lat_2=45 +lat_0=40 
> +lon_0=-97" wrf12km_nc_g152.shp wrf12km_nc.shp


I believe adding +towgs84=0,0,0 to the lcc definition would result in
a sphere to ellipsoid conversion being applied.  I will stress that this
is generally *not* what you want to do, though it is possible it might make
sense in your specific situation.

Best regards,
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    | Geospatial Programmer for Rent

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