[gdal-dev] How does GDAL's NetCDF driver determine the spatial reference system

Kyle Shannon ksshannon at gmail.com
Mon Aug 9 20:12:04 EDT 2010


James,
I added polar stereographic support to the trunk in r18931.  I believe I
added all the coordinate systems to be cf=1.4 compliant.  I did not have a
dataset to test it.  I did not backport these changes to 1.7 because I was a
new commiter.  I will test your file tomorrow on my 1.8dev machine.

kss

# ============================
Kyle Shannon
Physical Science Technician
RMRS Fire Sciences Lab
Fire, Fuels & Smoke - RWU 4405
5775 Highway 10 W.
Missoula, MT 59808
(406)829-6954
kshannon at fs.fed.us
# ============================


On Mon, Aug 9, 2010 at 5:50 PM, James Hiebert <hiebert at uvic.ca> wrote:

> Sure.  The ticket can be found here:
> https://trac.osgeo.org/gdal/ticket/3715
>
> ~James
>
> On Mon, Aug 09, 2010 at 03:13:59PM -0400, Lucena, Ivan wrote:
> > James,
> >
> > Could do file a ticked and upload a sample file on
> http://trac.osgeo.org/gdal/ ?
> >
> > Regards,
> >
> > Ivan
> >
> > James Hiebert wrote:
> > > Hi All,
> > >
> > > I'm trying to use GDAL (version 1.7.2 on Gentoo built with hdf5 and
> netcdf
> > > support) to read NetCDF files, but I'm a little unclear on how the
> NetCDF
> > > driver attempts to determine the georeferencing.
> > >
> > > The driver page here:
> > > http://www.gdal.org/frmt_netcdf.html
> > > states that it will attempt to read the metadata "spatial_ref" for a
> Well
> > > Know Text definition of the spatial reference (I assume that it means
> that
> > > it will try to use a global attribute of the NetCDF file named
> spatial_ref).
> > >
> > > Since this would be convenient for my application, I attempted to use
> GDAL
> > > this way without success.
> > >
> > > + I added a global attribute named "spatial_ref" with the WKT
> definition of
> > > the spatial reference system.
> > > + gdalinfo on the file still reports "Coordinate System is `'"
> > > + opening the file with the python bindings and calling
> dst.GetProjection()
> > >   returns a blank string (i.e. no projection information)
> > >
> > > The full listings of my spatial reference definition, the output of
> ncdump
> > > and gdalinfo and the output from the python session are listed below.
>  Can
> > > anyone tell me whether I'm doing something wrong, or should I not count
> on
> > > georeferencing being supported by the NetCDF driver?
> > >
> > > ~James
> > >
> > > james at basalt ~ $ ncatted -a
> spatial_ref,global,a,c,'PROJCS["unnamed",GEOGCS["Normal Sphere
> > >
> (r=6370997)",DATUM["unknown",SPHEROID["sphere",6370997,0]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433]],PROJECTION["Polar_Stereographic"],PARAMETER["latitude_of_origin",60],PARAMETER["central_meridian",263],PARAMETER["scale_factor",1],PARAMETER["false_easting",3925000],PARAMETER["false_northing",8325000]]'
> > > narccap_ecpc-20c3m-tasmin-ncep.nc
> narccap_ecpc-20c3m-tasmin-ncep-with-srs.nc
> > >
> > >
> > > james at basalt ~ $ ncdump -h narccap_ecpc-20c3m-tasmin-ncep-with-srs.nc
> > > netcdf narccap_ecpc-20c3m-tasmin-ncep-with-srs {
> > > dimensions:
> > >     xc = 123 ;
> > >     yc = 104 ;
> > >     time = UNLIMITED ; // (9496 currently)
> > >     bnds = 2 ;
> > > variables:
> > >     char polar_stereographic ;
> > >             polar_stereographic:grid_mapping_name =
> > > "polar_stereographic" ;
> > >             polar_stereographic:longitude_of_central_meridian = 263. ;
> > >             polar_stereographic:straight_vertical_longitude_from_pole =
> > > 263. ;
> > >             polar_stereographic:standard_parallel = 60. ;
> > >             polar_stereographic:TrueGridLength_Latitude = 60. ;
> > >             polar_stereographic:XGridLength_M = 50000. ;
> > >             polar_stereographic:YGridLength_M = 50000. ;
> > >             polar_stereographic:PoleOnPlane = "north" ;
> > >             polar_stereographic:false_easting = 3925000. ;
> > >             polar_stereographic:false_northing = 8325000. ;
> > >             polar_stereographic:latitude_of_projection_origin = 90. ;
> > >     double yc(yc) ;
> > >             yc:long_name = "y-coordinate of Cartesian system" ;
> > >             yc:standard_name = "projection_y_coordinate" ;
> > >             yc:axis = "Y" ;
> > >             yc:units = "m" ;
> > >     double xc(xc) ;
> > >             xc:long_name = "x-coordinate of Cartesian system" ;
> > >             xc:standard_name = "projection_x_coordinate" ;
> > >             xc:axis = "X" ;
> > >             xc:units = "m" ;
> > >     double lon(yc, xc) ;
> > >             lon:units = "degrees_east" ;
> > >             lon:long_name = "longitude" ;
> > >             lon:standard_name = "longitude" ;
> > >             lon:axis = "X" ;
> > >             lon:NX_NumPntsOnParallel = 123 ;
> > >             lon:NY_NumPntsOnMeridian = 104 ;
> > >             lon:actual_range = 211.5412f, 316.2759f ;
> > >             lon:XGridLength_M = 50000. ;
> > >             lon:YGridLength_M = 50000. ;
> > >             lon:PoleOnPlane = "north" ;
> > >     double lat(yc, xc) ;
> > >             lat:units = "degrees_north" ;
> > >             lat:long_name = "latitude" ;
> > >             lat:standard_name = "latitude" ;
> > >             lat:axis = "Y" ;
> > >             lat:NX_NumPntsOnParallel = 123 ;
> > >             lat:NY_NumPntsOnMeridian = 104 ;
> > >             lat:actual_range = 21.23807f, 67.63758f ;
> > >             lat:XGridLength_M = 50000. ;
> > >             lat:YGridLength_M = 50000. ;
> > >             lat:PoleOnPlane = "north" ;
> > > ...
> > >
> > > // global attributes:
> > > ...
> > >             :history = "Mon Aug  9 13:44:50 2010: ncatted -a
> > >             spatial_ref,global,a,c,PROJCS[\"unnamed\",GEOGCS[\"Normal
> > >             Sphere
> > >
> (r=6370997)\",DATUM[\"unknown\",SPHEROID[\"sphere\",6370997,0]],PRIMEM[\"Greenwich\",0],UNIT[\"degree\",0.0174532925199433]],PROJECTION[\"Polar_Stereographic\"],PARAMETER[\"latitude_of_origin\",60],PARAMETER[\"central_meridian\",263],PARAMETER[\"scale_factor\",1],PARAMETER[\"false_easting\",3925000],PARAMETER[\"false_northing\",8325000]]
> > >             narccap_ecpc-20c3m-tasmin-ncep.nc
> > >             narccap_ecpc-20c3m-tasmin-ncep-with-srs.nc\n",
> > >                     "Fri May  8 09:34:14 2009: ncrcat
> > > tasmin_ECPC_1979010106.nc tasmin_ECPC_1981010106.nc
> > > tasmin_ECPC_1986010106.nc tasmin_ECPC_1991010106.nc
> > > tasmin_ECPC_1996010106.nc tasmin_ECPC_2001010106.nc
> > > narccap_ecpc-20c3m-tasmin-ncep.nc" ;
> > >             :nco_openmp_thread_number = 1 ;
> > >             :spatial_ref = "PROJCS[\"unnamed\",GEOGCS[\"Normal Sphere
> > >
> (r=6370997)\",DATUM[\"unknown\",SPHEROID[\"sphere\",6370997,0]],PRIMEM[\"Greenwich\",0],UNIT[\"degree\",0.0174532925199433]],PROJECTION[\"Polar_Stereographic\"],PARAMETER[\"latitude_of_origin\",60],PARAMETER[\"central_meridian\",263],PARAMETER[\"scale_factor\",1],PARAMETER[\"false_easting\",3925000],PARAMETER[\"false_northing\",8325000]]"
> > > ;
> > > }
> > >
> > > james at basalt ~ $ gdalinfo narccap_ecpc-20c3m-tasmin-ncep-with-srs.nc
> > > Driver: netCDF/Network Common Data Format
> > > Files: narccap_ecpc-20c3m-tasmin-ncep-with-srs.nc
> > >        narccap_ecpc-20c3m-tasmin-ncep-with-srs.nc.aux.xml
> > > Size is 512, 512
> > > Coordinate System is `'
> > > Metadata:
> > > ...
> > >   NC_GLOBAL#history1=Original output in GRIB 1
> > >   NC_GLOBAL#history2=Contains modifications made to original data
> > >   NC_GLOBAL#history=Mon Aug  9 13:44:50 2010: ncatted -a
> > >   spatial_ref,global,a,c,PROJCS["unnamed",GEOGCS["Normal Sphere
> > >
> (r=6370997)",DATUM["unknown",SPHEROID["sphere",6370997,0]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433]],PROJECTION["Polar_Stereographic"],PARAMETER["latitude_of_origin",60],PARAMETER["central_meridian",263],PARAMETER["scale_factor",1],PARAMETER["false_easting",3925000],PARAMETER["false_northing",8325000]]
> > >   narccap_ecpc-20c3m-tasmin-ncep.nc
> > >   narccap_ecpc-20c3m-tasmin-ncep-with-srs.nc
> > > Fri May  8 09:34:14 2009: ncrcat tasmin_ECPC_1979010106.nc
> > > tasmin_ECPC_1981010106.nc tasmin_ECPC_1986010106.nc
> > > tasmin_ECPC_1991010106.nc tasmin_ECPC_1996010106.nc
> > > tasmin_ECPC_2001010106.nc narccap_ecpc-20c3m-tasmin-ncep.nc
> > >   NC_GLOBAL#nco_openmp_thread_number=1
> > >   NC_GLOBAL#spatial_ref=PROJCS["unnamed",GEOGCS["Normal Sphere
> > >
> (r=6370997)",DATUM["unknown",SPHEROID["sphere",6370997,0]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433]],PROJECTION["Polar_Stereographic"],PARAMETER["latitude_of_origin",60],PARAMETER["central_meridian",263],PARAMETER["scale_factor",1],PARAMETER["false_easting",3925000],PARAMETER["false_northing",8325000]]
> > > Subdatasets:
> > >   SUBDATASET_1_NAME=NETCDF:"narccap_ecpc-20c3m-tasmin-ncep-with-srs.nc
> ":lon
> > >   SUBDATASET_1_DESC=[104x123] longitude (64-bit floating-point)
> > >   SUBDATASET_2_NAME=NETCDF:"narccap_ecpc-20c3m-tasmin-ncep-with-srs.nc
> ":lat
> > >   SUBDATASET_2_DESC=[104x123] latitude (64-bit floating-point)
> > >   SUBDATASET_3_NAME=NETCDF:"narccap_ecpc-20c3m-tasmin-ncep-with-srs.nc
> ":time_bnds
> > >   SUBDATASET_3_DESC=[9496x2] time_bnds (64-bit floating-point)
> > >   SUBDATASET_4_NAME=NETCDF:"narccap_ecpc-20c3m-tasmin-ncep-with-srs.nc
> ":tasmin
> > >   SUBDATASET_4_DESC=[9496x104x123] air_temperature (32-bit
> floating-point)
> > > Corner Coordinates:
> > > Upper Left  (    0.0,    0.0)
> > > Lower Left  (    0.0,  512.0)
> > > Upper Right (  512.0,    0.0)
> > > Lower Right (  512.0,  512.0)
> > > Center      (  256.0,  256.0)
> > >
> > >
> > > james at basalt ~ $ python
> > >>>> from osgeo import gdal
> > >>>> dst = gdal.Open("narccap_ecpc-20c3m-tasmin-ncep-with-srs.nc")
> > >>>> dst.GetProjection()
> > >
> > > _______________________________________________
> > > gdal-dev mailing list
> > > gdal-dev at lists.osgeo.org
> > > http://lists.osgeo.org/mailman/listinfo/gdal-dev
> > >
> >
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