Emoslib is now deprecated

Geographical subareas can be created for new fields by defining latitude and longitude boundaries (North/West/South/East). However, subareas are not currently supported when creating reduced (quasi-regular) gaussian grids; for these, a full global grid is always produced. (Defining a suitable GRIB section 2 for reduced gaussian grid subareas can cause difficulties for application programs).

Global regular grids generated by interpolation have a longitude at 0 deg West. Latitude/longitude grids contain a line of latitude at the Equator, and gaussian grids are symmetrical about the Equator. Points within a subarea are based on the full global area and a requested subarea boundary may need to be adjusted to match the global area latitudes and longitudes. If a subarea boundary does not coincide with the full global area grid, the area is expanded outwards to a global grid line.

For example, if a latitude/longitude 6x6 degree grid is requested, global grid latitudes are generated at 90, 84, ..., 0, ..., -90 and longitudes at 0, 6, 12, .. . If a subarea is requested, its points must fit the global grid positions, so its latitude-longitude boundaries are compared with the underlying global grid and adjusted outwards so that the subarea is enclosed. For a 6x6 degree grid, a subarea of 87N/3W/81S/15E would expand to 90N/6W/84S/18E.