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

Limei Ran lran at unc.edu
Tue Sep 9 13:46:39 EDT 2008

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,
> 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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