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

[John C. Tull]

If your projections have epsg codes, you might use those instead. E.g.:
ogr2ogr -t_srs "EPSG:4326" -s_srs "EPSG:26911" outfile.shp infile.shp

You can check for epsg codes (or their equivalent wkt, proj4, etc.) at http://spatialreference.org 
.

Regards,
John

On Sep 9, 2008, at 10:46 AM, 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
>
> Thank you very much,
>
> Limei
>
>
>>
>> Limei,
>>
>> Generally speaking, when going between "real" datums and these  
>> spherical
>> based projections, the right thing to do is to apply no shift which  
>> is why
>> the default behavior was changed in PROJ 4.6.
>>
>> But to get consistent overlay, you really need to know quite a bit  
>> about
>> your data.
>>
>> Best regards,
>
>
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