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Thank you Dennis.
I'm using version 4.2.1, netcdf-cxx4 by Lynton Appel, on openSUSE 12.1, so
I think it's fairly up-to-date. The problem is not that I am unable to open
the file (I, too, can print out the 24 values), but that doing so
apparently uses ~19 mb of bandwidth, according to the iftop monitoring
utility. This seems quite excessive.
Please let me know if there is specific information that I should provide
here. Much appreciated,
Taylor
On Mon, Feb 18, 2013 at 5:57 PM, Dennis Heimbigner <dmh@xxxxxxxxxxxxxxxx>wrote:
>
> 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]<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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>
--
Taylor Binnington
e. tbinnington@xxxxxxxxx
c. 647 926 4144
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