The specific details of how the transformation (from spectral T255 to 0.25x0.25 lat-lon grid point for example) or regridding (from reduced Gaussian N128
to 0.25x0.25 lat-lon grid point) can be found in the EMOSLIB reference guide:
https://software.ecmwf.int/wiki/display/EMOS/Reference+Guide
In particular, the sections on Transformations (including any automatic truncation) and Grid point to Grid point Interpolation.
The sections on Land-Sea Masks and Precipitation also give information about "special" processing which is done for some parameters.
