[gradsusr] Problem with date line crossing data in netcdf files

Wed Feb 16 11:28:19 EST 2011

Because of that junk on the end of your longitude values, GrADS thinks  
your file has a non-linear X axis, which is probably causing these  
problems. Try overriding the metadata with a complete XDEF statement  
in a descriptor file and see if that changes anything.
--Jennifer

On Feb 15, 2011, at 10:59 PM, Frank Sonntag wrote:

> Hello,
>
> We've come across a problem when working with netcdf data from the  
> Ocean
> Forecast System. The grid spans the date line with longitudes from  
> 250 to 20
> degrees. The netcdf file is created by wgrib2.
> Printing out the longitude of the second (or later) point past the  
> date line
> gives the following error:
>
> ga-> set x 2200
> LON set to 4.92 4.92
> ga-> d lon
> Data Request Error: Invalid grid coordinates
>  World coordinates convert to non-integer  grid coordinates
>    Variable = lon  Dimension = 0
>  Error ocurred at column 1
> DISPLAY error:  Invalid expression
>  Expression = lon
>
>
> However the first point past the date line works:
> ga-> set x 2102
> LON set to 0.02 0.02
> ga-> d lon
> Printing Grid -- 1 Values -- Undef = -9.99e+08
> 0.02
>
>
>
> I have noticed that when handling netcdf files grads tests whether a  
> dimension
> is linear or in levels by comparing the differences between the  
> element 1 and
> 2 and 2 and 3 which in this case would yield a positive result.
> OTOH the longitudes generated by wgrib2 are not strictly linear, as  
> the
> following excerpt shows:
> 359.57, 359.62, 359.67, 359.72,
>    359.77, 359.82, 359.87, 359.92, 359.97, 0.0200000000000387,
>    0.07000000000005, 0.120000000000005, 0.170000000000016,
>    0.220000000000027, 0.270000000000039, 0.32000000000005,
>    0.370000000000005, 0.420000000000016, 0.470000000000027,
>    0.520000000000039, 0.57000000000005, 0.620000000000005,
>    0.670000000000016, 0.720000000000027, 0.770000000000039,
>    0.82000000000005, 0.870000000000005, 0.920000000000016,
>    0.970000000000027, 1.02000000000004, 1.07000000000005, 1.12,
>    1.17000000000002, 1.22000000000003, 1.27000000000004,  
> 1.32000000000005,
>    1.37, 1.42000000000002, 1.47000000000003, 1.52000000000004,
>    1.57000000000005, 1.62, 1.67000000000002, 1.72000000000003,
>    1.77000000000004, 1.82000000000005, 1.87, 1.92000000000002,
>    1.97000000000003, 2.02000000000004, 2.07000000000005, 2.12,
>    2.17000000000002, 2.22000000000003, 2.27000000000004,  
> 2.32000000000005,
>    2.37, 2.42000000000002, 2.47000000000003, 2.52000000000004,
>    2.57000000000005, 2.62, 2.67000000000002, 2.72000000000003,
>    2.77000000000004, 2.82000000000005, 2.87, 2.92000000000002,
>
>
> I am not sure if this is a bug in grads or expected behaviour but  
> would be
> grateful for any opinions on this or workarounds.
>
> I can provide a (800kb) test data file on request.
>
> Cheers,
> Frank
>
> Environment:
> GNU/Linux
>
> Config: v2.0.a8 little-endian readline printim grib2 netcdf hdf4-sds  
> hdf5
> opendap-grids,stn geotiff shapefile
> Grid Analysis and Display System (GrADS) Version 2.0.a8
> Copyright (c) 1988-2010 by Brian Doty and the
> Institute for Global Environment and Society (IGES)
> This program is distributed WITHOUT ANY WARRANTY
> See file COPYRIGHT for more information.
>
> Built Fri Mar 26 10:24:10 EDT 2010 for x86_64-unknown-linux-gnu
>
> This version of GrADS has been configured with the following options:
>  o Built on a LITTLE ENDIAN machine
>  o Athena Widget GUI DISABLED
>  o Command line editing ENABLED
>      http://tiswww.case.edu/php/chet/readline/rltop.html
>  o printim command for image output ENABLED
>      http://www.zlib.net
>      http://www.libpng.org/pub/png/libpng.html
>      http://www.libgd.org/Main_Page
>  o GRIB2 interface ENABLED
>      http://www.ijg.org
>      http://www.ece.uvic.ca/~mdadams/jasper
>      http://www.nco.ncep.noaa.gov/pmb/codes/GRIB2
>      g2clib-1.1.8
>  o NetCDF interface ENABLED
>      http://www.unidata.ucar.edu/software/netcdf
>      netcdf 4.1.1-rc2 of Mar 23 2010 09:31:58 $
>  o OPeNDAP gridded data interface ENABLED
>  o OPeNDAP station data interface ENABLED
>      http://iges.org/grads/gadoc/supplibs.html
>      libgadap 2.0
>  o HDF4 and HDF5 interfaces ENABLED
>      http://hdfgroup.org
>      HDF 4.2r3
>      HDF5 1.8.4
>  o GeoTIFF and KML output ENABLED
>      http://www.libtiff.org
>      http://geotiff.osgeo.org
>  o Shapefile interface ENABLED
>      http://shapelib.maptools.org
> _______________________________________________
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--
Jennifer M. Adams
IGES/COLA
4041 Powder Mill Road, Suite 302
Calverton, MD 20705
jma at cola.iges.org

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