ncmpidump - Convert netCDF files to ASCII form (CDL)
ncmpidump [-ch] [-v var1,...
] [-b lang
] [-l len
] [-n name
] [-p f_digits[,d_digits]
ncmpidump -k file
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
is a companion program that can generate a
binary netCDF file from a CDL file. Hence ncmpigen
can be used as inverses to transform the data representation between binary
and ASCII representations. See ncmpigen
for a description of CDL and
may also be used to determine what kind of netCDF file is used
(which variant of the netCDF file format) with the -k option.
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, ncmpidump
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
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.
uses `_' to represent data values that are equal to the
`_FillValue' attribute for a variable, intended to represent data that has not
yet been written. If a variable has no `_FillValue' attribute, the default
fill value for the variable type is used if the variable is not of byte type.
- 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.
- 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
- -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 ncmpigen -b
in generating a default netCDF file name. By default, ncmpidump
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
ncmpigen -b can be specified, it may be wise to have
ncmpidump change the default name to avoid inadvertantly
overwriting a valuable netCDF file when using ncmpidump, editing
the resulting CDL file, and using ncmpigen -b to generate a new
netCDF file from the edited CDL file.
- -p float_digits[,double_digits]
- Specifies default precision (number of significant digits) to use in
displaying floating-point or double precision data values for attributes
and variables. If specified, this value overrides the value of the
`C_format' attribute for any variable that has such an 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. In the absence of any
-p 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 -p 9,17 (according to Theorem 15 of
the paper listed under REFERENCES).
- Reports the kind of netCDF file: classic, 64-bit offset, or 64-bit data.
Before netCDF version 3.6, there was only one kind of netCDF file,
designated as `classic' (also know as format variant 1 or CDF-1). Large
file support introduced another variant of the format, designated as
`64-bit offset' (known as format variant 2 or CDF-2). Large data support
introduced another variant of the format, designated as `64-bit data'
(known as format variant 5 or CDF-5).
Look at the structure of the data in the netCDF file ` foo.nc
Produce an annotated CDL version of the structure and data in the netCDF file `
', using C-style indexing for the annotations:
ncmpidump -b c foo.nc > foo.cdl
Output data for only the variables `uwind' and `vwind' from the netCDF file `
', and show the floating-point data with only three significant
digits of precision:
ncmpidump -v uwind,vwind -p 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':
What Every Computer Scientist should Know About Floating-Point
ncmpidump -v omega -f fortran -n omega foo.nc > Z.cdl
, D. Goldberg, ACM Computing Surveys, Vol. 23, No. 1
March 1991, pp. 5-48.
$Date: 2013-11-17 00:21:28 -0600 (Sun, 17 Nov 2013) $
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
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.