Re: [thredds] NetCDF subsetting

Are new versions quite frequent, or has the CF reached a fairly stable
release?  I would like to use CF for a program, but if it changes frequently
I may have issues.

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@xxxxxxxxx
# ===================


On Tue, Feb 16, 2010 at 4:45 PM, Ethan Davis <edavis@xxxxxxxxxxxxxxxx>wrote:

> Hi Kyle,
>
> The "earth_radius" attribute was added to CF in version 1.2 (May 2008).
> The "spherical_earth_radius_meters" attribute pre-dates that CF version
> and our GRIB reading code hasn't been updated to reflect that change.
>
> We'll get that fixed and give our GRIB to CF code another look. We'll
> try to get any fixes on this into our next netCDF-java release (which
> will hopefully be in the next few days). If they don't make it into that
> release, they should be in the next one.
>
> Thanks,
>
> Ethan
>
> On 2/16/2010 1:31 PM, Kyle Shannon wrote:
> > Is there any reason why the radius tag is:
> "spherical_earth_radius_meters"
> > instead of the CF-1.0 tag:
> > "earth_radius"
> > ?
> >
> > 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@xxxxxxxxx <mailto:kshannon@xxxxxxxxx>
> > # ===================
> >
> >
> > On Mon, Feb 15, 2010 at 9:52 AM, John Caron <caron@xxxxxxxxxxxxxxxx
> > <mailto:caron@xxxxxxxxxxxxxxxx>> wrote:
> >
> >     Robb Kambic wrote:
> >
> >         On Tue, 9 Feb 2010, Kyle Shannon wrote:
> >
> >             Hello all,
> >             I am using the netCDF subsetting service on ucar's
> >             motherlode thredds
> >             server.  I am having an issue with the projection of the
> >             subset.
> >
> >             I run ncdump on the entire ndfd grid (full spatial extents)
> >             and get:
> >
> >             kyle@Lucky13:~/nc_issue$ ncdump -h ndfd_all.nc
> >             <http://ndfd_all.nc> | grep Lambert_Conformal
> >                    Maximum_temperature:grid_mapping = "Lambert_Conformal"
> ;
> >                char Lambert_Conformal ;
> >                    Lambert_Conformal:grid_mapping_name =
> >             "lambert_conformal_conic" ;
> >                    Lambert_Conformal:standard_parallel = 25. ;
> >                    Lambert_Conformal:longitude_of_central_meridian = 265.
> ;
> >                    Lambert_Conformal:latitude_of_projection_origin = 25.
> ;
> >                    Lambert_Conformal:earth_shape = "Earth spherical with
> >             radius
> >             specified by producer in m" ;
> >                    Lambert_Conformal:spherical_earth_radius_meters =
> >             6371200. ;
> >                    Lambert_Conformal:GRIB_param_Dx = 5079.361 ;
> >                    Lambert_Conformal:GRIB_param_Dy = 5079.472 ;
> >                    Lambert_Conformal:GRIB_param_GDSkey = 801839731 ;
> >                    *Lambert_Conformal:GRIB_param_La1 = 20.192 ;
> >                    Lambert_Conformal:GRIB_param_LaD = 25. ;
> >                    Lambert_Conformal:GRIB_param_Latin1 = 25. ;
> >                    Lambert_Conformal:GRIB_param_Latin2 = 25. ;
> >                    *Lambert_Conformal:GRIB_param_Lo1 = 238.446 ;
> >                    Lambert_Conformal:GRIB_param_LoV = 265. ;
> >                    Lambert_Conformal:GRIB_param_NpProj = "true" ;
> >                    Lambert_Conformal:GRIB_param_Nx = 1073 ;
> >                    Lambert_Conformal:GRIB_param_Ny = 689 ;
> >                    Lambert_Conformal:GRIB_param_ProjFlag = 0 ;
> >                    Lambert_Conformal:GRIB_param_Quasi = "false" ;
> >                    Lambert_Conformal:GRIB_param_ResCompFlag = 8 ;
> >                    Lambert_Conformal:GRIB_param_SpLat = -90. ;
> >                    Lambert_Conformal:GRIB_param_SpLon = 0. ;
> >                    Lambert_Conformal:GRIB_param_VectorComponentFlag =
> >             "gridRelative" ;
> >                    Lambert_Conformal:GRIB_param_Winds = "Relative" ;
> >                    Lambert_Conformal:GRIB_param_grid_name =
> >             "Lambert_Conformal" ;
> >
> >              Lambert_Conformal:GRIB_param_grid_radius_spherical_earth =
> >             6371200.
> >             ;
> >                    Lambert_Conformal:GRIB_param_grid_shape = "Earth
> >             spherical with
> >             radius specified by producer in m" ;
> >                    Lambert_Conformal:GRIB_param_grid_shape_code = 1 ;
> >                    Lambert_Conformal:GRIB_param_grid_type = 30 ;
> >                    Lambert_Conformal:GRIB_param_grid_units = "m" ;
> >                    Lambert_Conformal:GRIB_param_scanning_mode = 64 ;
> >                    Lambert_Conformal:_CoordinateTransformType =
> >             "Projection" ;
> >                    Lambert_Conformal:_CoordinateAxisTypes = "GeoX GeoY" ;
> >
> >             and when I run it on the subsetted data, I get:
> >
> >             kyle@Lucky13:~/nc_issue$ ncdump -h ndfd.nc <http://ndfd.nc>
> >             | grep Lambert_Conformal
> >                    Maximum_temperature:grid_mapping = "Lambert_Conformal"
> ;
> >                char Lambert_Conformal ;
> >                    Lambert_Conformal:grid_mapping_name =
> >             "lambert_conformal_conic" ;
> >                    Lambert_Conformal:standard_parallel = 25. ;
> >                    Lambert_Conformal:longitude_of_central_meridian = 265.
> ;
> >                    Lambert_Conformal:latitude_of_projection_origin = 25.
> ;
> >                    Lambert_Conformal:earth_shape = "Earth spherical with
> >             radius
> >             specified by producer in m" ;
> >                    Lambert_Conformal:spherical_earth_radius_meters =
> >             6371200. ;
> >                    Lambert_Conformal:GRIB_param_Dx = 5079.361 ;
> >                    Lambert_Conformal:GRIB_param_Dy = 5079.472 ;
> >                    Lambert_Conformal:GRIB_param_GDSkey = 801839731 ;
> >                    Lambert_Conformal:GRIB_param_La1 = 20.192 ;
> >                    Lambert_Conformal:GRIB_param_LaD = 25. ;
> >                    Lambert_Conformal:GRIB_param_Latin1 = 25. ;
> >                    Lambert_Conformal:GRIB_param_Latin2 = 25. ;
> >                    Lambert_Conformal:GRIB_param_Lo1 = 238.446 ;
> >                    Lambert_Conformal:GRIB_param_LoV = 265. ;
> >                    Lambert_Conformal:GRIB_param_NpProj = "true" ;
> >                    Lambert_Conformal:GRIB_param_Nx = 1073 ;
> >                    Lambert_Conformal:GRIB_param_Ny = 689 ;
> >                    Lambert_Conformal:GRIB_param_ProjFlag = 0 ;
> >                    Lambert_Conformal:GRIB_param_Quasi = "false" ;
> >                    Lambert_Conformal:GRIB_param_ResCompFlag = 8 ;
> >                    Lambert_Conformal:GRIB_param_SpLat = -90. ;
> >                    Lambert_Conformal:GRIB_param_SpLon = 0. ;
> >                    Lambert_Conformal:GRIB_param_VectorComponentFlag =
> >             "gridRelative" ;
> >                    Lambert_Conformal:GRIB_param_Winds = "Relative" ;
> >                    Lambert_Conformal:GRIB_param_grid_name =
> >             "Lambert_Conformal" ;
> >
> >              Lambert_Conformal:GRIB_param_grid_radius_spherical_earth =
> >             6371200.
> >             ;
> >                    Lambert_Conformal:GRIB_param_grid_shape = "Earth
> >             spherical with
> >             radius specified by producer in m" ;
> >                    Lambert_Conformal:GRIB_param_grid_shape_code = 1 ;
> >                    Lambert_Conformal:GRIB_param_grid_type = 30 ;
> >                    Lambert_Conformal:GRIB_param_grid_units = "m" ;
> >                    Lambert_Conformal:GRIB_param_scanning_mode = 64 ;
> >                    Lambert_Conformal:_CoordinateTransformType =
> >             "Projection" ;
> >                    Lambert_Conformal:_CoordinateAxisTypes = "GeoX GeoY" ;
> >                    Total_cloud_cover:grid_mapping = "Lambert_Conformal" ;
> >                    Wind_direction_from_which_blowing:grid_mapping =
> >             "Lambert_Conformal"
> >             ;
> >                    Wind_speed:grid_mapping = "Lambert_Conformal" ;
> >
> >             My question is, how can the latitude and longitude of the
> >             1st cell not
> >             change after the subsetting?  It appears that the meta data
> >             from the full
> >             dataset is just copied to the subset data.  Is this correct?
> >
> >
> >         Kyle,
> >
> >
> >     As Robb says, all the Lambert_Conformal:GRIB_XXXX attributes are
> >     simply copied over to the netcdf file from the GRIB GDS. We dont use
> >     these GRIB parameters for anything. Robb failed to mention that the
> >     actual coordinates are stored in the x and y coordinate variables in
> >     the netcdf file. In this case these are projection coordinates,
> >     which are converted to lat/lon values through the lambert conformal
> >     projection.  If you check the "include lat/lon" box, the 2D lat/lon
> >     coordinates will also be included in the file, as Robb indicates.
> >     This is needed to be in strict compliance with CF conventions, but
> >     is not needed by the CDM software.
> >
> >
> >
> >         Yes. The GDS parameters that you are looking at are the
> >         parameters for the model, so they are copied over to the
> >         resulting file. Usually users make the subsetting file name
> >         contain the latitude and longitude information of the subset.
> >
> >         How can I
> >
> >             figure out where my subset data is on the world?
> >
> >
> >         Click the check box on the sub-set page for "Add Lat/Lon to file"
> >         to the resulting file. Now the ncdump on the Lat and Lon
> >         variables will be available.
> >
> >         When you open/display the file the information will also be
> >         available.
> >
> >         On a programming level:
> >
> >         If you open the file as a GridDataset, you should be able to
> >         access the needed information. Here's an url about GridDatasets:
> >
> >
> http://www.unidata.ucar.edu/software/netcdf-java/tutorial/GridDatatype.html
> >
> >         You will also need to to look at the java-docs on the
> GridDataset.
> >
> >
> >         RObb...
> >
> >
> >             Thanks, sorry for the messy message.
>
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