Nathan,
Beautiful ! That is exactly what I am looking for. I can come
up with my own version of nccopy in Java or Python if I so wish. So that
means DAP2 can download netCDF files using the PSD THREDDS server and I
can pass OpeNDAP constraint expressions.
Regards,
Ashwin.
On Fri, May 27, 2016 at 7:17 PM, Nathan Potter <ndp@xxxxxxxxxxx> wrote:
>
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> Ashwin,
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> The NetCDF library may be useful for your desired outcome. Because the
> NetCDF library supports access via the DAP2 protocol it is a natural for
> your probelm. I was able to use the NetCDF command line tools to accomplish
> your task. Note that be dropping the “*.ascii*” suffix from the URL path
> you return to the core “DAP2 URL” which is an important step in the
> following example.
>
> Retrieving the data subset and saving it as a NetCDF-4 file:
>
> *./nccopy -4
>
> "http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/ncep.reanalysis2/pressure/air.2014.nc?air[480:603][2][20:34][26:40]
> <http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/ncep.reanalysis2/pressure/air.2014.nc?air[480:603][2][20:34][26:40]>”
> foo.nc <http://foo.nc>*
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> Which was easily read by ncdump:
>
> *./ncdump -h foo.nc <http://foo.nc>*
> *netcdf foo {*
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> *dimensions: time = UNLIMITED ; // (124 currently) lat = 15 ; level = 1 ;
> lon = 15 ;variables: short air(time, level, lat, lon) ; air:long_name =
> "6-hourly Air Temperature on Pressure Levels" ; air:valid_range = -32765s,
> -10260s ; air:unpacked_valid_range = 137.5f, 362.5f ; air:actual_range =
> 180.6f, 325.8f ; air:units = "degK" ; air:add_offset = 465.15f ;
> air:scale_factor = 0.01f ; air:missing_value = 32766s ; air:_FillValue =
> -32767s ; air:precision = 2s ; air:least_significant_digit = 1s ;
> air:GRIB_id = 11s ; air:GRIB_name = "TMP" ; air:var_desc = "Air
> temperature" ; air:dataset = "NCEP/DOE AMIP-II Reanalysis (Reanalysis-2)" ;
> air:level_desc = "Pressure Levels" ; air:statistic = "Individual Obs" ;
> air:parent_stat = "Other" ; air:standard_name = "air_temperature" ;//
> global attributes: :Conventions = "CF-1.0" ; :title = "4x Daily NCEP/DOE
> Reanalysis 2" ; :history = "created 2015/02 by NOAA/ESRL/PSD" ; :comments =
> "Data is from \nNCEP/DOE AMIP-II Reanalysis (Reanalysis-2)\n(4x/day). It
> consists of most variables interpolated to\npressure surfaces from model
> (sigma) surfaces." ; :platform = "Model" ; :source = "NCEP/DOE AMIP-II
> Reanalysis (Reanalysis-2) Model" ; :institution = "National Centers for
> Environmental Prediction" ; :References =
> "http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis2.html
> <http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis2.html>" ;
> :dataset_title = "NCEP-DOE AMIP-II Reanalysis" ;
> :DODS_EXTRA.Unlimited_Dimension = "time" ;}*
>
> I am sure that there are several other ways to achieve a similar result,
> but this one does seem simple and amenable to programatic (well, at least
> script level) use.
>
> I believe that both the NetCDF C and Java APIs will also happily detect
> that a supplied file name is a URL and then dereference and retrieve data
> from it.
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> Does this in any way address your problem?
>
> Regards,
>
> Nathan
>
>
>
> On May 27, 2016, at 2:13 AM, ashwinD12 . <winash12@xxxxxxxxx> wrote:
>
> Regarding the specifics of what you have written in relation to the
> programming language of choice
>
> 1) If I use java netcdf(the latest version) I can use the OPeNDAP URL that
> James explained to me and send it to the URL -
> http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/ncep.reanalysis2/pressure/air.2014.nc.ascii?air[480:603][2][20:34][26:40]
> (as
> an example)
> the data returned will be ascii but the java netcdf library will allow me
> to generate a netcdf file containing that data precisely that can be
> written to disk. Am I correct in this ?
>
> 2) The other option is to use the URL you gave me and generate the URL
> with the required parameters and then use Python and pycurl and write out
> the netcdf file to disk.
>
> Your input is appreciated,
> Regards,
> Ashwin.
>
>
> = = =
> Nathan Potter ndp at opendap.org
> OPeNDAP, Inc. +1.541.231.3317
>
>
