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[netCDFJava #VCW-324829]: why do variable values change when I convert from grib2 to netcdf?



Hi Larry:

1) its a grib1 file.

2) its likely that you are seeing differences between netcdf-java version 4.2 
and 4.5. Hopefully the 4.5 version is correct. 

3) The Originating Center is (200) Papua New Guinea, and we are using our best 
guess as to what tables they are using. You might want to look closely to see 
if they make sense, and let us know if they dont.

Regards,
John


> Sure.  Here it is.
> 
> I'm stumped.  I hope you have some idea what's going on!
> 
> Thanks,
> 
> Larry Mastin
> 
> address@hidden> wrote:
> 
> > that is a bit mysterious. can you send us the original grib file?
> >
> > > Dear Conduit support:
> > >
> > > I recently received some meteorological data files from Italian
> > colleagues
> > > that appear to be in Grib2 format.  I was able to convert them to netcdf
> > > format by typing:
> > >
> > > java -Xmx2048m -classpath ~/ncj/netcdfAll-4.5.jar
> > > ucar.nc2.dataset.NetcdfDataset \
> > > -in 2015_02_01_000.meteo -out 2015_02_01_000.nc
> > >
> > > Surprisingly however, the declarations and values of some of the
> > variables
> > > seem to change when I convert to netcdf.
> > >
> > > For example, I can view the "y" variable in the grib file by opening it
> > in
> > > ToolsUI-4.2.jar, right-clicking on variable y and choosing "ncdump."  I
> > get:
> > >
> > >
> > *****************************************************************************************************************************************************
> > >
> > > double y(y=101);
> > > :units = "degrees";
> > > :long_name = "y coordinate of projection";
> > > :standard_name = "projection_y_coordinate";
> > > :grid_spacing = "-9999.0 degrees";
> > > :_CoordinateAxisType = "GeoY";
> > >
> > > data:
> > >
> > > {-23.0, -10022.0, -20021.0, -30020.0, -40019.0, -50018.0, -60017.0,
> > > -70016.0, -80015.0, -90014.0, -100013.0, -110012.0, -120011.0, -130010.0,
> > > -140009.0, -150008.0, -160007.0, -170006.0, -180005.0, -190004.0,
> > > -200003.0, -210002.0, -220001.0, -230000.0, -239999.0, -249998.0,
> > > -259997.0, -269996.0, -279995.0, -289994.0, -299993.0, -309992.0,
> > > -319991.0, -329990.0, -339989.0, -349988.0, -359987.0, -369986.0,
> > > -379985.0, -389984.0, -399983.0, -409982.0, -419981.0, -429980.0,
> > > -439979.0, -449978.0, -459977.0, -469976.0, -479975.0, -489974.0,
> > > -499973.0, -509972.0, -519971.0, -529970.0, -539969.0, -549968.0,
> > > -559967.0, -569966.0, -579965.0, -589964.0, -599963.0, -609962.0,
> > > -619961.0, -629960.0, -639959.0, -649958.0, -659957.0, -669956.0,
> > > -679955.0, -689954.0, -699953.0, -709952.0, -719951.0, -729950.0,
> > > -739949.0, -749948.0, -759947.0, -769946.0, -779945.0, -789944.0,
> > > -799943.0, -809942.0, -819941.0, -829940.0, -839939.0, -849938.0,
> > > -859937.0, -869936.0, -879935.0, -889934.0, -899933.0, -909932.0,
> > > -919931.0, -929930.0, -939929.0, -949928.0, -959927.0, -969926.0,
> > > -979925.0, -989924.0, -999923.0}
> > >
> > >
> > *****************************************************************************************************************************************************
> > >
> > > In the netcdf file, I view the y variable by typing:
> > >
> > > $ncdump -v y 2015_02_01_000.nc
> > >
> > > When I do so, the y variable is declared as:
> > >
> > >
> > *****************************************************************************************************************************************************
> > > . . .
> > > float y(y) ;
> > > y:standard_name = "projection_y_coordinate" ;
> > > y:units = "km" ;
> > > . . .
> > >
> > *****************************************************************************************************************************************************
> > >
> > > And the values are given as:
> > >
> > >
> > *****************************************************************************************************************************************************
> > > data:
> > >
> > > y = -23, -22.9375, -22.875, -22.8125, -22.75, -22.6875, -22.625,
> > -22.5625,
> > > -22.5, -22.4375, -22.375, -22.3125, -22.25, -22.1875, -22.125,
> > > -22.0625,
> > > -22, -21.9375, -21.875, -21.8125, -21.75, -21.6875, -21.625, -21.5625,
> > > -21.5, -21.4375, -21.375, -21.3125, -21.25, -21.1875, -21.125,
> > > -21.0625,
> > > -21, -20.9375, -20.875, -20.8125, -20.75, -20.6875, -20.625, -20.5625,
> > > -20.5, -20.4375, -20.375, -20.3125, -20.25, -20.1875, -20.125,
> > > -20.0625,
> > > -20, -19.9375, -19.875, -19.8125, -19.75, -19.6875, -19.625, -19.5625,
> > > -19.5, -19.4375, -19.375, -19.3125, -19.25, -19.1875, -19.125,
> > > -19.0625,
> > > -19, -18.9375, -18.875, -18.8125, -18.75, -18.6875, -18.625, -18.5625,
> > > -18.5, -18.4375, -18.375, -18.3125, -18.25, -18.1875, -18.125,
> > > -18.0625,
> > > -18, -17.9375, -17.875, -17.8125, -17.75, -17.6875, -17.625, -17.5625,
> > > -17.5, -17.4375, -17.375, -17.3125, -17.25, -17.1875, -17.125,
> > > -17.0625,
> > > -17, -16.9375, -16.875, -16.8125, -16.75 ;
> > >
> > >
> > *****************************************************************************************************************************************************
> > >
> > > These y values are clearly different from the ones in the grib file.
> > >
> > > Is there some automatic change that happens when I convert from grib to
> > > netcdf using that java command?
> > >
> > > Thanks very much for your help.
> > >
> > > Sincerely,
> > >
> > > Larry Mastin
> > >
> > > --
> > > U.S. Geological Survey
> > > David A. Johnston Cascades Volcano Observatory
> > > 1300 SE Cardinal Court, Bldg. 10, Suite 100
> > > Vancouver, WA 98683 USA
> > > tel. (360) 993-8925
> > > fax (360) 993-8980
> > >
> > >
> >
> >
> > Ticket Details
> > ===================
> > Ticket ID: VCW-324829
> > Department: Support netCDF Java
> > Priority: Normal
> > Status: Open
> >
> >
> 
> 
> --
> U.S. Geological Survey
> David A. Johnston Cascades Volcano Observatory
> 1300 SE Cardinal Court, Bldg. 10, Suite 100
> Vancouver, WA 98683 USA
> tel. (360) 993-8925
> fax (360) 993-8980
> 
> 


Ticket Details
===================
Ticket ID: VCW-324829
Department: Support netCDF Java
Priority: Normal
Status: Closed