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Attributes may be associated with each netCDF variable to specify such
properties as units, special values, maximum and minimum valid values,
scaling factors, and offsets. Attributes for a netCDF file are
defined when the file is first created, while the netCDF file is in define
mode. Additional attributes may be added later by reentering define
mode. A netCDF attribute has a netCDF variable to which it is assigned,
a name, a type, a length, and a sequence of one or more values. An
attribute is designated by its variable ID and name, except in one case
(ncattname
or NCANAM
in FORTRAN), where attributes are
designated by variable ID and number because their names are unknown.
The attributes associated with a variable are typically defined right after the variable is created, while still in define mode. The data type, length, and value of an attribute may be changed even when in data mode, as long as the changed attribute requires no more space than the attribute as originally defined.
It is also possible to assign attributes not associated with any
variable to the netCDF as a whole, by using the NC_GLOBAL
variable
pseudo-ID. Global attributes may be used for purposes such as providing
a title or processing history for a netCDF data set.
Operations supported on attributes are:
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