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

[Matt Wilkie]

Hello All,

I've recently noticed that projecting with ogr2ogr (and I presume 
gdalwarp since they share so much) and using epsg codes adds information 
to .prj files that apparently proj doesn't know about. For example:

   # ogr2ogr -f "esri shapefile" -t_srs epsg:3579 (...)

will write this .prj (note "D_North_American_1983_CSRS98"):

   PROJCS["NAD83(CSRS) / Yukon 
Albers",GEOGCS["NAD83(CSRS)",DATUM["D_North_American_1983_CSRS98",SPHEROID["GRS_1980",6378137,298.257222101]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Albers"],PARAMETER["standard_parallel_1",61.66666666666666],PARAMETER["standard_parallel_2",68],PARAMETER["latitude_of_origin",59],PARAMETER["central_meridian",-132.5],PARAMETER["false_easting",500000],PARAMETER["false_northing",500000],UNIT["Meter",1]]

However asking proj to list the datums it knows about, there is nothing 
about NAD83CSRS:
   # proj -ld|grep -i --after-context=1 nad
   NAD83 GRS80   towgs84=0,0,0
                 North_American_Datum_1983
   NAD27 clrk66  nadgrids=@conus, at alaska, at ntv2_0.gsb, at ntv1_can.dat
                 North_American_Datum_1927

Environment:
    osgeo4w on WinXPx64
    Proj version: Rel. 4.6.1, 21 August 2008
    ogr2ogr version: unknown, but gdal utilities report "GDAL 1.5.4, 
released 2009/01/07"


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? 

cheers,

-- 
matt wilkie
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Geomatics Analyst
Information Management and Technology
Yukon Department of Environment
10 Burns Road * Whitehorse, Yukon * Y1A 4Y9
867-667-8133 Tel * 867-393-7003 Fax
http://environmentyukon.gov.yk.ca/geomatics/
--------------------------------------------