XIOS: Saving or loading interpolation weights

With the XIOS library one can define output domains (grid) which are different from input domains (grids), and XIOS does the necessary interpolation.

This requires, once source and destination grids are known, to compute some interpolation weights (during the initialization step). For large grids, this can take some time. One can however tell XIOS to save the interpolation weights in a file and use that file (if it is present) rather than recompute them when a new simulation is ran.

In practice one must add extra keys to the "interpolate_domain" tag, e.g.:

    <domain id="dom_256_192" type="rectilinear" ni_glo="256" nj_glo="192" >
      <generate_rectilinear_domain/>
      <interpolate_domain order="1" write_weight="true" mode="read_or_compute" />
    </domain>

This will automatically generate a NetCDF file containing the weights. Default file name will be something like xios_interpolation_weights_CONTEXT_INPUTDOMAIN_OUTPUTDOMAIN.nc , where CONTEXT, INPUTDOMAIN and OUTPUTDOMAIN are inherited from the context (i.e. definitions of these in the xml files).

One can specify the name of the file with the key "weight_filename", e.g.

    <domain id="dom_256_192" type="rectilinear" ni_glo="256" nj_glo="192" >
      <generate_rectilinear_domain/>
      <interpolate_domain order="1" write_weight="true" mode="read_or_compute" weight_filename="xios_weights" />
    </domain>

07/04/2022