[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: writing char string values

> Organization: University of Alaska
> Keywords: 199408060038.AA13541 netCDF char variables

Hi,

>  I have several variable length character strings to be stored in 
> non-record variables of a netcdf file.  I have seen the syntax for 
> storing character arrays in record variables but am having difficulty
> applying it to variables without dimension dependence.  Also, how should
> these non record strings be declared in the .cdl file?

Sorry to take so long to reply; I was on vacation.

There is a section entitled ``Reading and Writing Character String Values''
in the NetCDF User's Guide in the chapter on Variables that provides an
explanation and examples of writing character string values in non-record
variables.  This section also explains why character strings must be
modeled as character arrays in netCDF, with the character-position
dimension explicit.  In particular, this means that character-string valued
variables must be of fixed length, and if you don't want to waste space by
padding their values, you must use a separate dimension for each character
variable.  If you can store character values in netCDF attributes instead of
netCDF variables, the CDL syntax is much simpler and you don't need to
worry about providing explicit lengths or maximum lengths for character
strings.

Conventionally, character-position dimensions have names that have a
``_len'' of ``Len'' suffix, although this convention is not followed in the
examples in the NetCDF User's Guide.  There are some examples of netCDF
files that use string variables in the pub/netcdf/cdl/ directory on
ftp.unidata.ucar.edu, available via anonymous FTP.  For example, the
`staName' variable in `upperAir.cdl', and the `origin', `model', and
`navname' variables in `maps_hybrid_b.cdl' are non-record variables that
have character string values.  There are many other examples in the same
directory.

--
Russ Rew                                                   UCAR Unidata Program
address@hidden                                             P.O. Box 3000
http://www.unidata.ucar.edu/                             Boulder, CO 80307-3000