Re: [netcdfgroup] (no subject)

• To: Taylor Binnington <tbinnington@xxxxxxxxx>
• Subject: Re: [netcdfgroup] (no subject)
• From: Dennis Heimbigner <dmh@xxxxxxxxxxxxxxxx>
• Date: Mon, 18 Feb 2013 15:57:32 -0700

The opendap code in the netcdf-C libraries
(used by the C++ library) will in fact
properly handle the constraint you specified.
I just ran it and as expected, it is only pulling
in the 24 values you requested (took some 5 seconds to
obtain and print out the data).

One possibility is that you are using a rather old version
of the netcdf-C library.

=Dennis Heimbigner
 Unidata

Taylor Binnington wrote:

Hello,

I have an 'understanding' type of question. I have omitted details of my
OS, NetCDF installation, and a minimal example since I do not think they
are important for my question, but I can provide these details if they are
important.

When I attempt to open a MERRA file using the NetCDF C++ libraries, with a
line like the following, in my code:

NcFile datafile("
http://goldsmr2.sci.gsfc.nasa.gov/opendap/hyrax/MERRA/MAT1NXSLV.5.2.0/1990/01/MERRA100.prod.assim.tavg1_2d_slv_Nx.19900101.hdf?U50M_EOSGRID_Data_Fields[0:23][282:282][441:441]
",NcFile::read);

...I notice that quite a lot (nearly 20 MB) is being transferred from Hyrax
to my PC. However, all that I am interested in are the actual array values
(24 separate 32-bit real numbers) of the U50M_EOSGRID_Data_Fields. It has
been suggested that the entire array (of size 24*361*540 32-bit reals) is
being transferred by NetCDF before any subsetting takes place, is this
true? If so, is it then not possible to use OPeNDAP URLs to subset
on-the-fly through the NetCDF libraries?

Thank you for your help!
Taylor



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