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[netCDF #MKO-964114]: some questions

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  • Subject: [netCDF #MKO-964114]: some questions
  • Date: Thu, 03 May 2012 17:00:12 -0600
Hi Doug,

> I am a new user of netCDF and wish you could help me with my questions.
> 1. Within one netCDF file, can variables have different dimensions? In my 
> imagination, netCDF stores one variable (array) in one layer. Each layer may 
> not have relation with others. In this way, variables in one netCDF can have 
> different dimensions.

No, a single variable is defined to be a specific shape, determined by the list 
of dimensions
it uses.

However, netCDF-4 files have named "groups", and each group may have dimensions 
and variables
with the same names but different sizes or shapes as dimensions and variables 
in other groups.
It is analogous to the situation with files in directories, where the same name 
can refer to
different files in different directories of a hierarchical file system.

So maybe what you are calling "layers" are like netCDF-4 "groups".

> 2. When we create a netCDF file, do we have to put all data in the CDL file? 
> It may not be complex but time consuming. Can we link a well-defined external 
> file to the CDL file? For example, indicate the external fiel location on the 
> hard drive.

No, you don't need to use CDL files (which are human-readable text files).  
NetCDF files
(which are binary files) may be created directly with custom programs or 
utilities.
Typically, you either use a CDL file to create metadata, then the ncgen utility 
to turn
that into a binary netCDF file.  Or you use a program to create e netCDF file, 
then use
ncdump to see that as a CDL file.  But you don't need to manually modify a CDL 
file to
keep it consistent with a netCDF file (which I think you are asking about, if I 
understand
your question).

There is no standard or convention for including data by reference or linking 
in a binary
netCDF file, although you could store file names as values of string type 
attributes or
variables.  However, netCDF Java supports NcML files, which can store links to 
external
data in one or more other files, which can be netCDF files.  For more 
information about
NcML, and especially the use of NcML for aggregation, here:

  http://www.unidata.ucar.edu/software/netcdf/ncml/

--Russ

Russ Rew                                         UCAR Unidata Program
address@hidden                      http://www.unidata.ucar.edu



Ticket Details
===================
Ticket ID: MKO-964114
Department: Support netCDF
Priority: Normal
Status: Closed