DELFT-FEWS offers the possibility to import and/or export grid data by using the netcdf format. To standarize the format used for these netcdf-files a convention was designed. This convention will be described in this chapter. The basis for the DELFT-FEWS netcdf convention is the CF metadata convention. The DELFT-FEWS netcdf conventions restricts this convention by applying extra limitations on the format of the netcdf-files.
DELFT-FEWS supports importing data for rectangular grids and for non-rectangular grids. The import format used for a rectangular grid is differs from the format used for non-rectangular grids.
General- The variables must have exactly 3 dimensions: time,y,x (rectangular) or time,row,col(non-rectangular),
- The order of the dimensions is fixed and should also be time,y,x or time,row,col,
- The time-dimension is identified by its units-atribute. The units value must be a string formatted as per recommendations in the Udunits package. The name time is recommended but others name like date or t are also allowed,
- All dimensions have the axis-attribute which indicates which axis is defined with this dimension. For the time-axis the attribute should always be T. For the row- and y-dimension this attribute is Y. For the col- and x-dimension this attribute is X.
- Missing values can be indicated by using the _FillValue attribute or the missing_value attribute,
- Packaging of data is supported by defining an add_offset and/or a scale_factor for a variabele.
- The internal parameterids should be mapped to a name which is compliant with the CF metadata convention in the idmap-files,
- Per file only one time-variable, or x (col)- and y(row)-variable is allowed.
Rectangular grids
- Rectangular grids have 3 dimensions time,y,x. All the dimension are 1D. The y- and x-dimension must have the same geodatum as defined in the configuration (grids.xml).
Non-rectangular grids
- These grids have 3 dimensions time,row,col. The time-dimension is 1D. The row- and col-dimension are also 1D. The real x- and y-coordinates are stored in the variables y and x. y and x are both 2D variables and y(row,col) and x(row,col).