[netcdfgroup] Subsetting data with C++ API calls

• To: netcdfgroup <netcdfgroup@xxxxxxxxxxxxxxxx>
• Subject: [netcdfgroup] Subsetting data with C++ API calls
• From: Taylor Binnington <tbinnington@xxxxxxxxx>
• Date: Sun, 3 Mar 2013 16:34:23 -0500

Hello,

I'm attempting to read only certain parts (specific indices of specific
variable arrays), remotely, from a MERRA HDFEOS file.

I've recently upgraded to NetCDF 4.2.1.1, using Lynton's C++ library. At
first, I was using trying to subset the data directly from an OPeNDAP URL
supplied to NcFile, but it's been suggested to me, by an earlier post in
the OPeNDAP 
forums<https://groups.google.com/a/opendap.org/forum/?fromgroups=#!topic/opendap-tech/n7f2j0SRPL0>,
that this is not a good way to go. Instead, I should use NetCDF API calls.

I have carefully read through the C++ interface guide, including this
example:

http://www.unidata.ucar.edu/software/netcdf/docs/cxx4/test_var_8cpp-example.html

but am struggling to understand how to do this. A push in the right
direction would be very appreciated. The example (I don't fully understand
it, but was trying to emulate some of the example that I linked above)

#include <iostream>
#include <netcdf>
int main() {
NcFile dataFile("
http://goldsmr2.sci.gsfc.nasa.gov/opendap/hyrax/MERRA/MAT1NXSLV.5.2.0/1991/01/MERRA100.prod.assim.tavg1_2d_slv_Nx.19910101.hdf";,
NcFile::read);
NcGroup grouptest(dataFile.addGroup("Dataset"));
}

gives me the error:

terminate called after throwing an instance of
'netCDF::exceptions::NcNotNc4'
  what():  NcNotNc4: Attempting netcdf-4 operation on netcdf-3 file.
file: ncGroup.cpp  line:265
Aborted

This is not surprising, since the file is not a NetCDF-3 file.

Thank you in advance.
Taylor

-- 
Taylor Binnington
e. tbinnington@xxxxxxxxx

• Follow-Ups:
  • Re: [netcdfgroup] Subsetting data with C++ API calls
    • From: Lynnes, Christopher S. (GSFC-6102)