[gdal-dev] gdal/ogr/proj and NAD83(CSRS)

[Francesco P. Lovergine]

On Thu, Jul 23, 2009 at 10:13:42AM -0700, Matt Wilkie wrote:
> 
> I came across this curiosity while trying to figure out what the
> equivalent proj4 parameters were to epsg:3579. Using
> "+datum=nad83(csrs)" and combinations thereof result in
> "datum_unknown" being written to the .prj file.
> ((if there are no equivalent proj4 strings for the NAD83(CSRS)
> datum, then the proj4 reference files at spatialreference.org are in
> error and should probably be removed, or something.))
> 
> So now I'm wondering if transforming a file with gdal/ogr actually
> results in NAD83(CSRS) data, or if it really puts out NAD83 and
> blindly writes out the epsg code?
> 

I suspect EPSG does not define a NAD83(CSRS) datum because it needs
a dynamic reference frame definition, which cannot be approximated
decently with a seven parameters transformation, anyway. 
So it would be not a proper approach.

See 

ftp://geod.nrcan.gc.ca/pub/GSD/craymer/pubs/nad83_hydroscan2006.pdf
ftp://geod.nrcan.gc.ca/pub/GSD/craymer/pubs/nad83_geomatica2006.pdf

for reference. Maybe someone more expert on the proj list could be more 
precise about that.

-- 
Francesco P. Lovergine