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Re: 20030626:HDF -> netCDF

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  • Subject: Re: 20030626:HDF -> netCDF
  • Date: Sun, 13 Jul 2003 19:15:21 -0600
>To: address@hidden
>From: Raghavendra Prasad <address@hidden>
>Subject: Re: 20030428: subject
>Organization: ?
>Keywords: time conventions

G Raghavendra,

>  Can you kindly give me the syntax of putting time
> data into a netCDF file.
> 
>  My requirement is as follow:
> 
> ncid = nccreate("sst.nc", NC_CLOBBER);
> lonid = ncdimdef(ncid,"lon",4096);
> latid = ncdimdef(ncid,"lat",2048);
> sstid = ncdimdef(ncid,"sst",4096*2048);
> tineid = ncdimdef(ncid,"time",); 

I assume you meant to provide the size of the time dimensions as the
"unlimited" dimension, which can grow as you add more times to the
data.  in that case, you want something like:

 timeid = ncdimdef(ncid,"time",NC_UNLIMITED); 

where "NC_UNLIMITED" is a constant defined in the the netcdf.h file to
represent the dimension in a netCDF file that can increase in size.
 
> Please tell me how to put time as 1/1/1999 00:00:00 to
> 1/1/1999 23:59:59. I am under great pressure.

There are various conventions for representing time in netCDF files,
and which one you choose depends on what kinds of times you need to
represent.

I assume you want time to be a coordinate dimension, which means you
also need a "time" variable with the same name as the time dimension,
and it should have a "units" attribute that uses valid udunits syntax
for time, for example:

  double time(time);
     time:units = "seconds since 1999-01-01 00:00:00";

which would permit very precise time values.  Alternatively, if you
only need time values within an hour, for example, you could use
something like

  int time(time);
     time:units = "hours since 1999-01-01 00:00:00";

You should follow a published convention for how to represent time in
a netCDF file.  A good example is the CF Conventions for Climate and
Forecast Metadata:

  http://www.cgd.ucar.edu/cms/eaton/cf-metadata/CF-working.html

or the COARDS Conventions:

  http://ferret.wrc.noaa.gov/noaa_coop/coop_cdf_profile.html

Also see the netCDF Frequently Asked Question, "What is the best way
to handle time using netCDF?": 

  http://www.unidata.ucar.edu/packages/netcdf/faq.html#time

--Russ

_____________________________________________________________________

Russ Rew                                         UCAR Unidata Program
address@hidden                      http://my.unidata.ucar.edu