[GRASS-user] Help with export netCDF file

GRASS GRASS user
,
1

Hi all,

I really don’t have a problem with exporting a netCDF file from GRASS 8.4, but because of the intended use of the output file, I need to have variable name defined specifically, instead of the generic Band1:

ncdump -h sac_UZTWM.nc

netcdf sac_UZTWM {
dimensions:
x = 2698 ;
y = 2427 ;
variables:
double Band1(y, x) ;
Band1:long_name = “GDAL Band Number 1” ;
Band1:_FillValue = -999. ;
Band1:grid_mapping = “lambert_conformal_conic” ;
Band1:COLOR_TABLE_RULES_COUNT = 255 ;
Band1:COLOR_TABLE_RULE_RGB_0 = “0.000000e+00 5.496153e-01 68 1 84 68 2 86” ;
Band1:COLOR_TABLE_RULE_RGB_1 = “5.496153e-01 1.099231e+00 68 2 86 69 4 87” ;
Band1:COLOR_TABLE_RULE_RGB_2 = “1.099231e+00 1.648846e+00 69 4 87 69 5 89” ;
Band1:COLOR_TABLE_RULE_RGB_3 = “1.648846e+00 2.199863e+00 69 5 89 70 7 90” ;
Band1:COLOR_TABLE_RULE_RGB_4 = “2.199863e+00 2.749479e+00 70 7 90 70 8 92” ;
Band1:COLOR_TABLE_RULE_RGB_5 = “2.749479e+00 3.299094e+00 70 8 92 70 10 93” ;
Band1:COLOR_TABLE_RULE_RGB_6 = “3.299094e+00 3.848709e+00 70 10 93 70 11 94” ;
Band1:COLOR_TABLE_RULE_RGB_7 = “3.848709e+00 4.398325e+00 70 11 94 71 13 96” ;

I need what I have below, using Climate Data Operators (cdo)…

cdo -chname,Band1,sac_UZTWM sac_UZTWM.nc sac_UZTWM.nc.test

I can change the variable name, which is exactly what I need:

ncdump -h sac_UZTWM.nc
netcdf sac_UZTWM {
dimensions:
x = 2698 ;
y = 2427 ;
variables:
double x(x) ;
x:standard_name = “projection_x_coordinate” ;
x:long_name = “x coordinate of projection” ;
x:units = “m” ;
x:axis = “X” ;
double y(y) ;
y:standard_name = “projection_y_coordinate” ;
y:long_name = “y coordinate of projection” ;
y:units = “m” ;
y:axis = “Y” ;
char lambert_conformal_conic ;
lambert_conformal_conic:grid_mapping_name = “lambert_conformal_conic” ;
lambert_conformal_conic:longitude_of_central_meridian = 74. ;
lambert_conformal_conic:false_easting = 0. ;
lambert_conformal_conic:false_northing = 0. ;
lambert_conformal_conic:latitude_of_projection_origin = 23. ;
lambert_conformal_conic:standard_parallel = 33., 45. ;
lambert_conformal_conic:long_name = “CRS definition” ;
lambert_conformal_conic:longitude_of_prime_meridian = 0. ;
lambert_conformal_conic:semi_major_axis = 6378137. ;
lambert_conformal_conic:inverse_flattening = 298.257223563 ;
lambert_conformal_conic:crs_wkt = “PROJCS["unknown",GEOGCS["wgs84",DATUM["WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]]],PROJECTION["Lambert_Conformal_Conic_2SP"],PARAMETER["latitude_of_origin",23],PARAMETER["central_meridian",74],PARAMETER["standard_parallel_1",33],PARAMETER["standard_parallel_2",45],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH]]” ;
lambert_conformal_conic:spatial_ref = “PROJCS["unknown",GEOGCS["wgs84",DATUM["WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]]],PROJECTION["Lambert_Conformal_Conic_2SP"],PARAMETER["latitude_of_origin",23],PARAMETER["central_meridian",74],PARAMETER["standard_parallel_1",33],PARAMETER["standard_parallel_2",45],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH]]” ;
lambert_conformal_conic:GeoTransform = "-1567000 1000 0 2160000 0 -1000 " ;
double sac_UZTWM(y, x) ;
sac_UZTWM:long_name = “GDAL Band Number 1” ;
sac_UZTWM:grid_mapping = “lambert_conformal_conic” ;
sac_UZTWM:_FillValue = -999. ;
sac_UZTWM:missing_value = -999. ;

// global attributes:
:CDI = “Climate Data Interface version 2.4.0 (https://mpimet.mpg.de/cdi)” ;
:Conventions = “CF-1.5” ;
:GDAL = “GDAL 3.9.3, released 2024/10/07 (debug build)” ;
:history = “Tue Feb 25 06:31:46 2025: cdo -chname,Band1,sac_UZTWM sac_UZTWM.nc sac_UZTWM.nc.test\n”,
“Tue Feb 25 06:30:38 2025: GDAL Create( /media/teaiii/research/pakistan/parameters/sac_UZTWM.nc, … )” ;
:CDO = “Climate Data Operators version 2.4.0 (https://mpimet.mpg.de/cdo)” ;
}

But how using r.out.gdal can I do this; I tried something that I thought should work, but I got an error

r.out.gdal -c -m --overwrite input=uztwm@teaiii output=/media/teaiii/research/pakistan/parameters/sac_UZTWM.nc format=netCDF nodata=-999

Thank you,
Tom

2

Thomas

I have not tested, but have you looked into the “createopt” parameter in r.out.gdal?

From the manual:
“createopt=string[,string,…]
Creation option(s) to pass to the output format driver
In the form of “NAME=VALUE”, separate multiple entries with a comma”

So I believe that in principle you could pass the “BAND_NAMES” creation option from GDAL.

See:

https://gdal.org/en/stable/drivers/raster/netcdf.html#creation-options

https://grass.osgeo.org/grass85/manuals/r.out.gdal.html

Hope this helps

Hernán

···

Den 2025-02-25 kl. 17:26, skrev Thomas Adams via grass-user:

Hi all,

I really don’t have a problem with exporting a netCDF file from GRASS 8.4, but because of the intended use of the output file, I need to have variable name defined specifically, instead of the generic Band1:

ncdump -h sac_UZTWM.nc

netcdf sac_UZTWM {
dimensions:
x = 2698 ;
y = 2427 ;
variables:
double Band1(y, x) ;
Band1:long_name = “GDAL Band Number 1” ;
Band1:_FillValue = -999. ;
Band1:grid_mapping = “lambert_conformal_conic” ;
Band1:COLOR_TABLE_RULES_COUNT = 255 ;
Band1:COLOR_TABLE_RULE_RGB_0 = “0.000000e+00 5.496153e-01 68 1 84 68 2 86” ;
Band1:COLOR_TABLE_RULE_RGB_1 = “5.496153e-01 1.099231e+00 68 2 86 69 4 87” ;
Band1:COLOR_TABLE_RULE_RGB_2 = “1.099231e+00 1.648846e+00 69 4 87 69 5 89” ;
Band1:COLOR_TABLE_RULE_RGB_3 = “1.648846e+00 2.199863e+00 69 5 89 70 7 90” ;
Band1:COLOR_TABLE_RULE_RGB_4 = “2.199863e+00 2.749479e+00 70 7 90 70 8 92” ;
Band1:COLOR_TABLE_RULE_RGB_5 = “2.749479e+00 3.299094e+00 70 8 92 70 10 93” ;
Band1:COLOR_TABLE_RULE_RGB_6 = “3.299094e+00 3.848709e+00 70 10 93 70 11 94” ;
Band1:COLOR_TABLE_RULE_RGB_7 = “3.848709e+00 4.398325e+00 70 11 94 71 13 96” ;

I need what I have below, using Climate Data Operators (cdo)…

cdo -chname,Band1,sac_UZTWM sac_UZTWM.nc sac_UZTWM.nc.test

I can change the variable name, which is exactly what I need:

ncdump -h sac_UZTWM.nc
netcdf sac_UZTWM {
dimensions:
x = 2698 ;
y = 2427 ;
variables:
double x(x) ;
x:standard_name = “projection_x_coordinate” ;
x:long_name = “x coordinate of projection” ;
x:units = “m” ;
x:axis = “X” ;
double y(y) ;
y:standard_name = “projection_y_coordinate” ;
y:long_name = “y coordinate of projection” ;
y:units = “m” ;
y:axis = “Y” ;
char lambert_conformal_conic ;
lambert_conformal_conic:grid_mapping_name = “lambert_conformal_conic” ;
lambert_conformal_conic:longitude_of_central_meridian = 74. ;
lambert_conformal_conic:false_easting = 0. ;
lambert_conformal_conic:false_northing = 0. ;
lambert_conformal_conic:latitude_of_projection_origin = 23. ;
lambert_conformal_conic:standard_parallel = 33., 45. ;
lambert_conformal_conic:long_name = “CRS definition” ;
lambert_conformal_conic:longitude_of_prime_meridian = 0. ;
lambert_conformal_conic:semi_major_axis = 6378137. ;
lambert_conformal_conic:inverse_flattening = 298.257223563 ;
lambert_conformal_conic:crs_wkt = “PROJCS["unknown",GEOGCS["wgs84",DATUM["WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]]],PROJECTION["Lambert_Conformal_Conic_2SP"],PARAMETER["latitude_of_origin",23],PARAMETER["central_meridian",74],PARAMETER["standard_parallel_1",33],PARAMETER["standard_parallel_2",45],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH]]” ;
lambert_conformal_conic:spatial_ref = “PROJCS["unknown",GEOGCS["wgs84",DATUM["WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]]],PROJECTION["Lambert_Conformal_Conic_2SP"],PARAMETER["latitude_of_origin",23],PARAMETER["central_meridian",74],PARAMETER["standard_parallel_1",33],PARAMETER["standard_parallel_2",45],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH]]” ;
lambert_conformal_conic:GeoTransform = "-1567000 1000 0 2160000 0 -1000 " ;
double sac_UZTWM(y, x) ;
sac_UZTWM:long_name = “GDAL Band Number 1” ;
sac_UZTWM:grid_mapping = “lambert_conformal_conic” ;
sac_UZTWM:_FillValue = -999. ;
sac_UZTWM:missing_value = -999. ;

// global attributes:
:CDI = “Climate Data Interface version 2.4.0 (https://mpimet.mpg.de/cdi)” ;
:Conventions = “CF-1.5” ;
:GDAL = “GDAL 3.9.3, released 2024/10/07 (debug build)” ;
:history = “Tue Feb 25 06:31:46 2025: cdo -chname,Band1,sac_UZTWM sac_UZTWM.nc sac_UZTWM.nc.test\n”,
“Tue Feb 25 06:30:38 2025: GDAL Create( /media/teaiii/research/pakistan/parameters/sac_UZTWM.nc, … )” ;
:CDO = “Climate Data Operators version 2.4.0 (https://mpimet.mpg.de/cdo)” ;
}

But how using r.out.gdal can I do this; I tried something that I thought should work, but I got an error

r.out.gdal -c -m --overwrite input=uztwm@teaiii output=/media/teaiii/research/pakistan/parameters/sac_UZTWM.nc format=netCDF nodata=-999

Thank you,
Tom

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