Netcdf Writing 1d array into 2d array

Question

I am using code similar to this - Read in coordinate variables to read in latitude and longitude from a netCDF file

call check( nf_inq_varid(ncid, LAT_NAME, lat_varid) )
call check( nf_inq_varid(ncid, LON_NAME, lon_varid) )

! Read the latitude and longitude data.

call check( nf_get_var(ncid, lat_varid, lats) )
call check( nf_get_var(ncid, lon_varid, lons) )

Both lats and lons are 1-Dimensional fortran arrays.

My initial data set is in geographical coordinates and I need to convert this into a rotated lat lon grid and I use the code in this URL Geographical to rotated lat lon grid.

The way this works is the following For each geographical latitude and longitude I get a rotated latitude. Ditto for rotated longitude.

Mathematically

f(latitude_geo,longitude_geo) = latitude_rot
f(latitude_geo,longitude_geo) = longitude_rot

So the rotated lat and lon arrays are two dimensional arrays. I want to be able to write the rotated lat and lon arrays back to the original netCDF file using nf_put_vara_real or nf_90_put_vara_real(f77 or f90 does not matter).

How can I do this since the original lat and lon arrays are 1-D arrays ? Is it possible to read the original 1-d arrays as 2-D arrays ?

makra makra · Accepted Answer · 2016-09-06T09:28:30

Your transformation creates 2-dimensional longitude and latitude values, so you need to define x and y as new running indices.

lon(lon) => lon(x,y)
lat(lat) => lat(x,y)

Basically, you describe the lon and lat as variable and add x and y as new dimensions. This way longitude and latitudes are mapped to the correct grid points.

If written correctly to a NetCDF file, it's content should be similar to this one:

netcdf example {
dimensions:
        x = 360 ;
        y = 180 ;
variables:
        float x(x):
              x:long_name = "x-dimension" ;

        float y(y):
              y:long_name = "y-dimension" ;

        float lon(y, x) ;
                lon:long_name = "longitude" ;
                lon:units = "degrees_east" ;
                ...

        float lat(y, x) ;
                lat:long_name = "latitude" ;
                lat:units = "degrees_north" ;
                ...

        float data(y, x) ;
                data:long_name = "your data name" ;
                ...
}

(Output via ncdump -h example.nc)

Netcdf Writing 1d array into 2d array

1 Answers