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 nadgri...@conus,@alaska,@ntv2_0.gsb,@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
--------------------------------------------
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/
--------------------------------------------
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