ncdump-hdf(1)
NAME
ncdump-hdf - Convert netCDF files to ASCII form (CDL)
SYNOPSIS
ncdump-hdf [-c] [-h] [-v var1,...] [-b lang] [-f lang] [-l len] [-n
name] [-d f_digits[,d_digits]] file
DESCRIPTION
ncdump-hdf generates an ASCII representation of a specified netCDF file
on standard output. The ASCII representation is in a form called CDL
(``network Common Data form Language'') that can be viewed, edited, or
serve as input to ncgen. ncgen is a companion program that can
generate a binary netCDF file from a CDL file. Hence ncgen and ncdump-
hdf can be used as inverses to transform the data representation
between binary and ASCII representations. See ncgen for a description
of CDL and netCDF representations.
ncdump-hdf defines a default format used for each type of netCDF data,
but this can be changed if a `C_format' attribute is defined for a
netCDF variable. In this case, ncdump-hdf will use the `C_format'
attribute to format each value. For example, if floating-point data
for the netCDF variable `Z' is known to be accurate to only three
significant digits, it would be appropriate to use the variable
attribute
Z:C_format = "%.3g"
ncdump-hdf may also be used as a simple browser for netCDF data files,
to display the dimension names and sizes; variable names, types, and
shapes; attribute names and values; and optionally, the values of data
for all variables or selected variables in a netCDF file.
OPTIONS
-c Show the values of coordinate variables (variables that are also
dimensions) as well as the declarations of all dimensions,
variables, and attribute values. Data values of non-coordinate
variables are not included in the output. This is the most
suitable option to use for a brief look at the structure and
contents of a netCDF file.
-h Show only the header information in the output, that is the
declarations of dimensions, variables, and attributes but no
data values for any variables. The output is identical to using
the -c option except that the values of coordinate variables are
not included. (At most one of -c or -h options may be present.)
-v var1,...,varn
The output will include data values for the specified variables,
in addition to the declarations of all dimensions, variables,
and attributes. One or more variables must be specified by name
in the comma-delimited list following this option. The list
must be a single argument to the command, hence cannot contain
blanks or other white space characters. The named variables
must be valid netCDF variables in the input-file. The default,
without this option and in the absence of the -c or -h options,
is to include data values for all variables in the output.
-b lang
A brief annotation in the form of a CDL comment (text beginning
with the characters ``//'') will be included in the data section
of the output for each `row' of data, to help identify data
values for multidimensional variables. If lang begins with `C'
or `c', then C language conventions will be used (zero-based
indices, last dimension varying fastest). If lang begins with
`F' or `f', then Fortran language conventions will be used (one-
based indices, first dimension varying fastest). In either
case, the data will be presented in the same order; only the
annotations will differ. This option is useful for browsing
through large volumes of multidimensional data.
-f lang
Full annotations in the form of trailing CDL comments (text
beginning with the characters ``//'') for every data value
(except individual characters in character arrays) will be
included in the data section. If lang begins with `C' or `c',
then C language conventions will be used (zero-based indices,
last dimension varying fastest). If lang begins with `F' or
`f', then Fortran language conventions will be used (one-based
indices, first dimension varying fastest). In either case, the
data will be presented in the same order; only the annotations
will differ. This option may be useful for piping data into
other filters, since each data value appears on a separate line,
fully identified.
-l len Changes the default maximum line length (80) used in formatting
lists of non-character data values.
-n name
CDL requires a name for a netCDF data set, for use by ncgen -b
in generating a default netCDF file name. By default, ncdump-
hdf constructs this name from the last component of the pathname
of the input netCDF file by stripping off any extension it has.
Use the -n option to specify a different name. Although the
output file name used by ncgen -b can be specified, it may be
wise to have ncdump-hdf change the default name to avoid
inadvertently overwriting a valuable netCDF file when using
ncdump-hdf, editing the resulting CDL file, and using ncgen -b
to generate a new netCDF file from the edited CDL file.
-d float_digits[,double_digits]
Specifies default number of significant digits to use in
displaying floating-point or double precision data values for
variables that don't have a `C_format' attribute. Floating-
point data will be displayed with float_digits significant
digits. If double_digits is also specified, double-precision
values will be displayed with that many significant digits. If
a variable has a `C_format' attribute, that overrides any
specified floating-point default. In the absence of any -d
specifications, floating-point and double-precision data are
displayed with 7 and 15 significant digits respectively. CDL
files can be made smaller if less precision is required. If
both floating-point and double-presision precisions are
specified, the two values must appear separated by a comma (no
blanks) as a single argument to the command. If you really want
every last bit of precision from the netCDF file represented in
the CDL file for all possible floating-point values, you will
have to specify this with -d 9,17 (according to Theorem 15 of
the paper listed under REFERENCES).
EXAMPLES
Look at the structure of the data in the netCDF file `foo.nc':
ncdump-hdf -c foo.nc
Produce an annotated CDL version of the structure and data in the
netCDF file `foo.nc', using C-style indexing for the annotations:
ncdump-hdf -b c foo.nc > foo.cdl
Output data for only the variables `uwind' and `vwind' from the netCDF
file `foo.nc', and show the floating-point data with only three
significant digits of precision:
ncdump-hdf -v uwind,vwind -d 3 foo.nc
Produce a fully-annotated (one data value per line) listing of the data
for the variable `omega', using Fortran conventions for indices, and
changing the netCDF dataset name in the resulting CDL file to `omega':
ncdump-hdf -v omega -f fortran -n omega foo.nc > Z.cdl
REFERENCES
What Every Computer Scientist should Know About Floating-Point
Arithmetic, D. Goldberg, ACM Computing Surveys, Vol. 23, No. 1, March
1991, pp. 5-48.
SEE ALSO
ncgen(1), netcdf(3)
BUGS
Character arrays that contain a null-byte are treated like C strings, so no characters after the null byte appear in the output. Multidimensional character string arrays are not handled well, since the CDL syntax for breaking a long character string into several shorter lines is weak. There should be a way to specify that the data should be displayed in `record' order, that is with the all the values for `record' variables together that have the same value of the record dimension. Printed: 116-$Date: 1996-03-26 16:34:11 -0600 (Tue, 26 Mar 1996) $ NCDUMP(1)
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