CDO

Hi Niklas,

here is an example:

Create data on hpz6:
cdo -f nc topo,hpz6 topo_hpz6.nc

Upgrate to hpz7:
cdo hpupgrade,nside=128 topo_hpz6.nc topo_hpz7.nc

Perfext, Uwe and Thanks a lot,
This works. The data I got was created using this:

cdo -f nc -setgridtype,unstructured -select,timestep=1,name=tas file:///fastdata/ka1081/nextgems_cycle3/ngc3028/ngc3028_P1D_8.zarr/#mode=zarr,file z8.nc

And then I tried using cdo to upgrade like this:

cdo hpupgrade,nside=512 z8.nc z9.nc
cdo hpupgrade (Abort): Input grid is not healpix!

ncdump -h shows:

netcdf z8 {
dimensions:
        time = UNLIMITED ; // (1 currently)
        ncells = 786432 ;
        vertices = 4 ;
variables:
        int time(time) ;
                time:standard_name = "time" ;
                time:units = "seconds since 1970-01-01" ;
                time:calendar = "proleptic_gregorian" ;
                time:axis = "T" ;
        float lon(ncells) ;
                lon:standard_name = "longitude" ;
                lon:long_name = "longitude" ;
                lon:units = "radian" ;
                lon:bounds = "lon_bnds" ;
        float lon_bnds(ncells, vertices) ;
        float lat(ncells) ;
                lat:standard_name = "latitude" ;
                lat:long_name = "latitude" ;
                lat:units = "radian" ;
                lat:bounds = "lat_bnds" ;
        float lat_bnds(ncells, vertices) ;
        float tas(time, ncells) ;
                tas:standard_name = "air_temperature" ;
                tas:long_name = "temperature in 2m" ;
                tas:units = "K" ;
                tas:CDI_grid_type = "unstructured" ;
                tas:coordinates = "lat lon" ;
                tas:cell_methods = "time: mean cell: mean" ;
                tas:component = "atmo" ;
                tas:vgrid = "height_2m" ;

Thanks and Cheers, Niklas

Ok, "-setgridtype,unstructured" will convert the healpix to unstructured data. Try:

cdo -f nc -select,timestep=1,name=tas file:///fastdata/ka1081/nextgems_cycle3/ngc3028/ngc3028_P1D_8.zarr/#mode=zarr,file z8.nc
cdo hpupgrade,nside=512 z8.nc z9.nc

Thanks Uwe, that makes sense. Is there a way to also have the cell coordinates, to properly reconstruct and position the grid for visualization? That was the beauty with using unstructured. I can of course write something to generate this, but maybe I am not the first one with this need.
Thanks and Cheers, Niklas

Yes, you can allways create the coordinates with "-setgridtype,unstructured" if needed:

cdo -setgridtype,unstructured -hpupgrade,nside=512 z8.nc z9.nc

Damns, that's too simple. ;-)
I managed to write a script that computes the coordinates for me, but yours is way more elegant. Thanks. I'll be quiet now.