wiki:Ticket107Text9Nov13Properties

Please don't modify this page. It is an annex to ticket 107 comment 2.

The other properties recognised by this CF data model correspond to attributes listed in CF Appendix A. For field constructs, the allowed properties are comment, history, institution, long_name, references, source, standard_error_multiplier, standard_name, title, units. For dimensions and auxiliary coordinate constructs, the allowed properties are axis, calendar, leap_month, leap_year, long_name, month_lengths, positive, standard_name, units. Coordinate constructs of time are optionally climatological; this property is indicated by the presence of the climatology attribute. In any field, any given value of the axis attribute can occur no more than once among all the dimension and auxiliary coordinates of that field. The CF data model allows field, dimension and auxiliary coordinate constructs to have other properties not defined by CF, provided they do not conflict with CF, but since they are not part of the CF standard, the data model does not provide any interpretation of them.

The attributes valid_max, valid_min and valid_range of data variables and coordinate variables are checks on the validity of the values, which could be verified on input and written on output. In this CF data model we assume they do not constrain any manipulations which might be done on the data in memory, and they are not part of the data model.

The attributes _FillValue and missing_value of data variables specify how missing data is indicated in the data array. This data model supports the idea of missing data, but does not depend on any particular method of indicating it, so these attributes are not part of the model.

The attributes add_offset, compress, flag_masks, flag_meanings, flag_values and scale_factor are all used in methods of compressing the data to save space in CF-netCDF files, with or without loss of information. They are not part of this data model because these operations do not logically alter the data, except that the compress attribute implies two alternative interpretations of coordinates (compressed or uncompressed).

The featureType attribute and associated conventions provide a way of packing multiple fields of the same kind of discrete sampling geometry (timeseries, trajectories, etc.) into a single CF-netCDF data variable, in order to save space, since a multidimensional representation with common coordinate variables is typically very wasteful in such cases. This is a kind of compression. The data model regards each instance of the feature type as an independent field construct. The featureType attribute is a property of each of these field constructs.

The attributes bounds, cell_measures, cell_methods, climatology, Conventions, coordinates, formula_terms and grid_mapping have various special or structural functions in the CF-netCDF file format. Their functions and the relationships they indicate are reflected in the structure of this data model, and these attributes do not correspond directly to properties in the data model.

Last modified 5 years ago Last modified on 11/09/13 14:46:45