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Re: 20030203: An example of netCDF with Grace

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  • Subject: Re: 20030203: An example of netCDF with Grace
  • Date: Mon, 03 Feb 2003 13:07:29 -0700
>To: address@hidden
>From: "murad ali" <address@hidden>
>Subject: An example of netCDF with Grace
>Organization: UCAR/Unidata
>Keywords: 200302031457.h13Evv624684

Hi Murad,

> I m Murad Ali from Pakistan.I have Installed Grace Sw, But I m un
> able to understand how to enter data / Communicate with it Via
> netCDf. Kindly send me An EXAMPLE for doing this. I will be very
> thank ful to you for this Kindeness.

There is a simple example of a netCDF file representing a simple
function of one variable here:

  ftp://ftp.unidata.ucar.edu/pub/netcdf/sample_data/xy.nc

The file "xy.nc" is a binary file in netCDF format that represents two
variables, x and y, where y is a function of x (in this case y =
x*x).  Here is the text form of this data:

 netcdf xy {  // simple file with a function of one variable
 dimensions:
    x = 10;
 variables:
    float x(x);  // coordinate variable
    float y(x);
 data:
    x = 0,  0.5, 1, 2,  2.5, 3,  4,  5,  7,  8;
    y = 0, 0.25, 1, 4, 6.25, 9, 16, 25, 49, 64;
 }

The notation above is called "CDL" and is the text form of the netCDF
file in xy.nc.  If you install the netCDF software, it comes with a
utility program "ncdump" that produces readable CDL from the binary
netCDF files.  Another utility program "ncgen" creates binary netCDF
files from the readable CDL files.  So one way to create netCDF files,
if you don't want to write a program that uses the netCDF library, is
to use a text editor to create a CDL file, then use the "ncgen"
utility program to generate a binary netCDF file from the CDL file.

Once you have a netCDF file, such as xy.nc above, you should be able
to use Grace to plot it.  For example,

  grace -netcdfxy x y xy.nc

should plot y versus x with the netCDF file example you can get using
the URL above.

There are many other ways to create netCDF files, using the library
and one of the language interfaces, for example Fortran77, C, C++
Fortran90, Java Perl, Python, or Ruby.  You can access information
about netCDF or various language interfaces to netCDF files from the
netCDF web site at

  http://my.unidata.ucar.edu/content/software/netcdf/index.html

--Russ

_____________________________________________________________________

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