[R-sig-Geo] Clip smaller domain from large domain netCDF file

[Aseem Sharma]

Hi Michael, Thank you and regrets for poor questioning and typo. I mean
ncdf4.
Yes the .nc file has three variables namely precipitation, Tmin and Tmax
with their time series. I can read it using raster.
the print function give details of data as below.
(NC_FORMAT_NETCDF4_CLASSIC):"
[1] ""
[1] "     3 variables (excluding dimension variables):"
[1] "        float pr[lon,lat,time]   "
[1] "            standard_name: precipitation_flux"
[1] "            long_name: Precipitation"
[1] "            units: mm day-1"
[1] "            _FillValue: -32768"
[1] "            cell_methods: time: mean"
[1] "        float tasmax[lon,lat,time]   "
[1] "            standard_name: air_temperature"
[1] "            long_name: Daily Maximum Near-Surface Air Temperature"
[1] "            units: degC"
[1] "            _FillValue: -32768"
[1] "            cell_methods: time: maximum"
[1] "        float tasmin[lon,lat,time]   "
[1] "            standard_name: air_temperature"
[1] "            long_name: Daily Minimum Near-Surface Air Temperature"
[1] "            units: degC"
[1] "            _FillValue: -32768"
[1] "            cell_methods: time: minimum"
[1] ""
[1] "     3 dimensions:"
[1] "        lon  Size:1068"
[1] "            standard_name: longitude"
[1] "            long_name: longitude"
[1] "            units: degrees_east"
[1] "            axis: X"
[1] "        lat  Size:510"
[1] "            standard_name: latitude"
[1] "            long_name: latitude"
[1] "            units: degrees_north"
[1] "            axis: Y"
[1] "        time  Size:22280   *** is unlimited ***"
[1] "            standard_name: time"
[1] "            long_name: time"
[1] "            units: days since 1950-01-01 00:00:00"
[1] "            calendar: standard"

I am trying to using netCDf tools in ncdf4 but not figure out how to do so.
Thank you,



------------------

"Namaste नमस्ते"

Aseem Sharma

Graduate Research Assistant

Northern Hydrometeorology Group(NHG)

Natural Resources and Environmental Studies Institute(NRESi)

University of Northern British Columbia

Prince George, BC, V2N 4Z9, Canada

Tel: 250-960-5427

Web: http://www.unbc.ca/


 "All know the Way, but few actually walk it."
"सबैको कल्याण होस् ।"




On Tue, Aug 26, 2014 at 4:59 PM, Michael Sumner <mdsumner at gmail.com> wrote:

> First see if raster can open it:
>
> library(raster)
> r <- raster("/path/to/hugefile.nc")
> r
>
> That will require you have the ncdf4 package installed (I don't know
> of any such package "netCDF4").
>
> If that works, try to crop with
>
> rc <- crop(r, extent(-130, -120, 50, 60))
>
> possibly with an added filename argument, e.g.
>
> rc <- crop(r, extent(-130, -120, 50, 60), filename =
> "/different/physical/disk/out.grd")
>
> But, this assumes you are only reading one slice in a possibly 3D or
> even 4D data set. 30Gb suggests that you are dealing with at least a
> time series here, so please report on the first attempt with raster.
> You must also have some idea of what is in there so please include
> that in your queries here.
>
> If raster can't deal with it you'll need to use the general NetCDF
> tools in ncdf4, so start with its documentation.
>
> And please read the posting guide.
>
> Cheers, Mike.
>
>
> On Wed, Aug 27, 2014 at 9:48 AM, Aseem Sharma <nature.aseem at gmail.com>
> wrote:
> > Hi,
> > I have this huge ( ~30GB) .nc file (NC_FORMAT_NETCDF4_CLASSIC)) for the
> > whole country 141.00 to 52.00 W, 41.00 to 84.00 N".
> > I am trying to clip this big dataset for a small region specific domain
> > (120.00 to 130.00 W, 50.00 to 60.00 N).
> > I am trying to do using netCDF4 r package but could not figure out how to
> > do so.
> > Kindly please suggest me how should i proceed.
> >
> >
> > Thank you,
> >
> >         [[alternative HTML version deleted]]
> >
> > _______________________________________________
> > R-sig-Geo mailing list
> > R-sig-Geo at r-project.org
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>
>
>
> --
> Michael Sumner
> Software and Database Engineer
> Australian Antarctic Division
> Hobart, Australia
> e-mail: mdsumner at gmail.com
>

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