Wrong grid on NetCDF to GRIB conversion

Hi CDO team,

I've been using CDO successfully to convert Lambert Conformal Conic NetCDF files to GRIB2 like this:

cdo -f grb2 copy in.nc out.grb

However, I now encountered strange behavior where for a 200-m resolution NetCDF file, the resulting GRIB2 grid seems incorrect. Here's the grid description for the source NetCDF file:

$ cdo griddes in.nc
#
# gridID 1
#
gridtype  = projection
gridsize  = 50000
xsize     = 250
ysize     = 200
xname     = x
xunits    = "m" 
yname     = y
yunits    = "m" 
xvals     = -3.72529029846191e-09 199.587681240402 399.945036566816 599.024267312139 
            799.385158726946 998.979852784425 1198.83229321986 1397.66247153655 1598.03042823169 
            ... many rows omitted for brevity
yvals     = 1.62981450557709e-09 199.014222515048 398.70365596097 598.730049135862 
            797.740483938949 1000.11186205386 1199.45798648917 1399.1410636201 1600.15574228903 
            ... many rows omitted for brevity
scanningMode = 64
grid_mapping = Lambert_Conformal
grid_mapping_name = lambert_conformal_conic
standard_parallel = 35.31035f
longitude_of_central_meridian = 75.f
latitude_of_projection_origin = 35.31035f
earth_radius = 6367470.
longitudeOfFirstGridPointInDegrees = 139.215f
latitudeOfFirstGridPointInDegrees = 35.30643f
cdo    griddes: Processed 5 variables [0.00s 51MB].

And here's the grid description for the target GRIB file:

t$ cdo griddes out.grb
#
# gridID 1
#
gridtype  = projection
gridsize  = 50000
xsize     = 250
ysize     = 200
xname     = x
xunits    = "m" 
yname     = y
yunits    = "m" 
xfirst    = 0
xinc      = 1.44
yfirst    = -89.55
yinc      = 0.9
scanningMode = 64
grid_mapping = Lambert_Conformal
grid_mapping_name = lambert_conformal_conic
standard_parallel = 35.310352
longitude_of_central_meridian = 75.
latitude_of_projection_origin = 35.310352
earth_radius = 6367470.
false_easting = -5424972.821748
false_northing = -1820872.47506838
longitudeOfFirstGridPointInDegrees = 139.215027
latitudeOfFirstGridPointInDegrees = 35.306431
cdo    griddes: Processed 5 variables [0.29s 81MB].

Based on xfirst, xinc, yfirst, and yinc, it seems to me that the target grid has x axis linearly spaced from approx. 0 to 360, and y axis from approx. -90 to 90. Instead, I expected xfirst and yfirst to be approx. 0 and xinc and yinc to be approx. 200.

I attach my in.nc and out.grb files. Any help or suggestions would be much appreciated.

Thank you!
Milan

Download all files

out.grb (977 KB) out.grb
in.nc (982 KB) in.nc

Replies (3)

RE: Wrong grid on NetCDF to GRIB conversion - Added by Milan Curcic over 3 years ago

This is my CDO build:

$ cdo -V
Climate Data Operators version 1.9.9rc1 (https://mpimet.mpg.de/cdo)
System: x86_64-pc-linux-gnu
CXX Compiler: g++ -g -O2 -fdebug-prefix-map=/build/cdo-51aH2m/cdo-1.9.9~rc1=. -fstack-protector-strong -Wformat -Werror=format-security -fopenmp 
CXX version : g++ (Ubuntu 9.2.1-28ubuntu1) 9.2.1 20200203
C Compiler: gcc -g -O2 -fdebug-prefix-map=/build/cdo-51aH2m/cdo-1.9.9~rc1=. -fstack-protector-strong -Wformat -Werror=format-security -Wall -pedantic -fPIC  -fopenmp  
C version : gcc (Ubuntu 9.2.1-28ubuntu1) 9.2.1 20200203
F77 Compiler: f77 -g -O2 -fdebug-prefix-map=/build/cdo-51aH2m/cdo-1.9.9~rc1=. -fstack-protector-strong
F77 version : unknown
Features: 7GB 4threads C++14 Fortran DATA PTHREADS OpenMP HDF5 NC4/HDF5/threadsafe OPeNDAP SZ UDUNITS2 PROJ MAGICS CURL FFTW3 SSE2
Libraries: HDF5/1.10.4 proj/6.3.0 curl/7.68.0(h7.66.0)
Filetypes: srv ext ieg grb1 grb2 nc1 nc2 nc4 nc4c nc5 
     CDI library version : 1.9.9rc1
 ecCodes library version : 2.16.0
  NetCDF library version : 4.7.3 of Jan 23 2020 04:18:16 $
    hdf5 library version : library undefined
    exse library version : 1.4.1
    FILE library version : 1.8.3

Thank you,
Milan

RE: Wrong grid on NetCDF to GRIB conversion - Added by Uwe Schulzweida over 3 years ago

Hi Milan,

It looks like there are problems with the inaccurate x and y values. I will take a closer look. You can work around the problem by using the following grid description:

cat > mygrid << EOR
gridtype  = projection
xsize     = 250
ysize     = 200
xname     = x
xunits    = "m" 
yname     = y
yunits    = "m" 
xfirst    = 0
xinc      = 200
yfirst    = 0
yinc      = 200
grid_mapping = Lambert_Conformal
grid_mapping_name = lambert_conformal_conic
standard_parallel = 35.31035f
longitude_of_central_meridian = 75.f
latitude_of_projection_origin = 35.31035f
earth_radius = 6367470.
longitudeOfFirstGridPointInDegrees = 139.215f
latitudeOfFirstGridPointInDegrees = 35.30643f
EOR

cdo -f grb2 setgrid,mygrid in.nc out.grb

Cheers,
Uwe

RE: Wrong grid on NetCDF to GRIB conversion - Added by Milan Curcic over 3 years ago

Uwe,

You rock--it works. Thanks a lot!

Milan

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