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Re: NPOESS Sample Files

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  • Subject: Re: NPOESS Sample Files
  • Date: Wed, 09 Nov 2005 20:17:09 -0700
Ted,

> Interest in the Common Data Model developments continues to grow in NOAA 
> and CLASS. I think you know that the NPP and NPOESS Programs have 
> decided to use HDF5 as their standard data format. Our goal would be to 
> have these files be readable using the NetCDF libraries. I realize that 
> there is a very small chance that that will be possible, but am 
> continuing to try to increase that probability. The NPOESS program 
> recently released some sample HDF5 files. I am wondering if you might be 
> able to take a look at these files and evaluate how they are written 
> with that goal in mind.

The AMS paper on netCDF-4 that we just referenced on the netcdfgroup
mailing list 

   http://www.unidata.ucar.edu/software/netcdf/papers/2006-ams.pdf

mentioned the HDF5 files for NPP and NPOESS and also described the
conditions under which an HDF5 file will be accessible through the
netCDF-4 interface in version 4.0:

    It is possible to create data using the HDF5
  interfaces that cannot be accessed through netCDF-4
  interfaces, because the netCDF-4 model is intentionally
  simpler. For example, with HDF5 it is possible to create
  a group containment cycle in which each of two groups
  contain the other. As another example, HDF5 has a
  reference data type, used for indirection much like
  pointers in C, but HDF5 references are not supported in
  netCDF-4.

    Nevertheless, it is practical to create HDF5 files that
  are accessible through the netCDF-4 interface, if the
  files are restricted to use only features supported by
  netCDF-4 and if the new HDF5 "dimension scales"
  feature is used to model shared dimensions. Following
  this advice is equivalent to using the Common Data
  Model, which is intended to be a more interoperable
  subset of data types and structures that will map easily
  to several interfaces. The netCDF-4 documentation
  accompanying the first release will contain more
  guidance about use of the Common Data Model.

Do you have details on how to access the NPP/NPOESS sample files?
We'll look at them when we get a chance, but I doubt that they use the
new "dimension scales" feature of HDF5, which is currently required
for accessing the data through netCDF-4 interfaces.

--Russ