fillWriter Options

The fillWriter enables the filling of an existing template-file with real data. It was developed to speed up creation of output-files of NWP-models. These models usually create output one timestep at a time and at the end, and the timesteps are then merged at another stage, often on another machine. Fimex fillWriter makes sure, that one can look at the final file even before the model is finished. It is even possible to restart the model at any state, replacing ony the newly created slices.

How to use the FillWriter

The axes of the output should well-known before model-start and the output-template should be written by e.g.

  fimex --input.file=example.nc input.printNcML=template.ncml
  # eventually add axes values or similar to ncml-file
  fimex --input.file=template.ncml --output.file=template.nc --output.type=nc4

This can also be achieved with more tuning possibilities with ncdump -s and ncgen -b.

Warning: ncgen until 4.2.1.1 has some bugs when using 'special' attributes. Please use ncgen >= 4.3.

netcdf fillIn2 {
dimensions:
    time = UNLIMITED ; // (2 currently)
    sigma = 5 ;
    lon = 3 ;
    lat = 4 ;
variables:
    short time(time) ;
        time:standard_name = "time" ;
        time:units = "hours since 2000-01-01 00:00:00 +00:00" ;
        time:_Storage = "chunked" ;
        time:_ChunkSizes = 1 ;
    short sigma(sigma) ;
        sigma:standard_name = "atmosphere_sigma_coordinate" ;
        sigma:positive = "up" ;
        sigma:scale_factor = 0.001f ;
        time:_Storage = "chunked" ;
        time:_ChunkSizes = 1 ;
    short lon(lon) ;
        lon:units = "degrees_east";
    short lat(lat) ;
        lat:units = "degrees_north";
    short cloud_area_fraction(time, sigma, lat, lon);
        cloud_area_fraction:units = "%";
        cloud_area_fraction:_Storage = "chunked";
        cloud_area_fraction:_ChunkSizes = 1, 1, 4, 3 ;
        cloud_area_fraction:_Shuffle = "true" ;
        cloud_area_fraction:_DeflateLevel = 3 ;
// global attributes:
        :Conventions = "CF-1.4" ;
        :_Format = "netCDF-4 classic model" ;
data:
 time = 12, 24 ;
 sigma = 200, 300, 500, 850, 1000 ;
 lon = -10, 0, 10;
 lat = 58, 59, 60, 61;
}

In particular when writing compressed netcdf-4 files, make sure to set the _ChunkSize to match the usual output-size, e.g. horizontal size when reading from grib-files. When creating the template with fimex from ncml, this is done automatically.

The usage of the program is then very simple:

  fimex --input.file=in.nc --output.fillFile=outFill.nc

See also: MetNoFimex::FillWriter fimex Program Options