7.0 Other methods
and examining netCDF files
Obtaining ascii output of
a netcdf file is possible. There are several methods. First is to use
ncdump or ncBrowse. Both ncdump and ncBrowse produce the ascii output
in the same format. However this format is not particulary friendly if
you want to import the data to a spreadsheet such as Excel. The second
method is to use Ferret, MATLAB or IDL. An example is given from Ferret
below. The third method is to use publicly available routines such as
I have not tested either of these routines.
This utility is a very useful
program for those who do not have Matlab, IDL, Ferret, or ncBrowse and want
to check the attributes and obtain the data from a netCDF file. On unix machines
the man pages describe this command in detail (and its partner ncgen) or in
the netCDF User's Guide for Fortran, (Chapter 10). To obtain the attributes
of the current meter data one would
>ncdump -h rcm00683.cdf
3 shows the output from this command. To obtain the speed data in this file
>ncdump -v speed rcm00683.cdf
or to obtain the speed and
the direction data
>ncdump -v speed,direction
The last command can lead
to large files ascii files, but have a relatively simple structure and can be
read by programs. However, the value of ncdump is that it allows one to check
attributes and structure of netcdf files quickly and easily. A more convenient
way to examine netCDF files is too be able to visualise the data using a graphical
interface such as ncBrowse or Ferret.
7.2 Using Ferret to create
Ferret has the capability
to read netcdf file directly, and it also has the capability to export variables
in ascii format from a netcdf file. For example the ferret commands
will use the sea-surface
temperature netcdf file (USE command), plot its contours (SHADE), and
list the sea-surface temperature field along the equator around the world to
the file called sea_surface_temperature (LIST).
The output of the LIST command
in this case is a more friendly format than the output from ncdump, and can
be imported into spreadsheet programs like excel, staroffice or gnumeric.
sea surface temperature (1/100 degree C)
LATITUDE: 0 (interpolated)
DATA SET: ./sst05d19900108.nc
0.25E / 1: 32767.
0.75E / 2: 32767.
1.25E / 3: 17644.
1.75E / 4: 32767.
2.25E / 5: 32767.
2.75E / 6: 17704.
3.25E / 7: 32767.
3.75E / 8: 32767.
4.25E / 9: 32767.
4.75E / 10: 32767.
0.25W / 720: 17711.
0.25E / 721: 32767.
0.75E / 722: 32767.
1.25E / 723: 17644.
1.75E / 724: 32767.
2.25E / 725: 32767.
2.75E / 726: 17704.
3.25E / 727: 32767.
Note that ferret cannot
list a large number of columns to a file, and thus the size of two dimensional
arrays that are LISTed to a file is limited.