Provided by: netcdf-bin_4.1.3-7ubuntu2_amd64 
NAME
ncdump - Convert netCDF file to text form (CDL)
SYNOPSIS
ncdump [-c] [-h] [-v var1,...] [-b lang] [-f lang] [-l len] [-n name] [-p
f_digits[,d_digits]] [-k] [-x] [-s] [-t] file
DESCRIPTION
ncdump generates a text representation of a specified netCDF file on standard output. The
text 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 can be used as
inverses to transform the data representation between binary and text representations.
See ncgen for a description of CDL and netCDF representations.
As of NetCDF version 4.1, and if DAP support was enabled when ncdump was built, the file
name may specify a DAP URL. This allows ncdump to print out data sources from DAP servers.
When used with the -h option, ncdump can be used to show the translation from the DAP DDS
data model to the NetCDF data model.
ncdump defines a default display 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
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 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.
ncdump 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.
ncdump may also be used to determine what kind of netCDF file is used (which variant of
the netCDF file format) with the -k option.
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 unless escaped. The named variables must be valid netCDF
variables in the input-file. A variable within a group in a netCDF-4 file may be
specified with an absolute path name, such as `/GroupA/GroupA2/var'. Use of a
relative path name such as `var' or `grp/var' specifies all matching variable names
in the 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 constructs this name from the last
component of the path name 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 change the
default name to avoid inadvertently overwriting a valuable netCDF file when using
ncdump, editing the resulting CDL file, and using ncgen -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-precision
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).
-k Show what kind of netCDF file the pathname references, one of `classic', `64-bit
offset',`netCDF-4', or `netCDF-4 classic model'. Before version 3.6, there was
only one kind of netCDF file, designated as `classic' (also know as format variant
1). Large file support introduced another variant of the format, designated as
`64-bit offset' (known as format variant 2). NetCDF-4, uses a third variant of the
format, `netCDF-4' (format variant 3). Another format variant, designated
`netCDF-4 classic model' (format variant 4), is restricted to features supported by
the netCDF-3 data model but represented using the HDF5 format, so that an
unmodified netCDF-3 program can read or write the file just by relinking with the
netCDF-4 library. The string output by using the `-k' option may be provided as
the value of the `-k' option to ncgen(1) to specify exactly what kind of netCDF
file to generate, when you want to override the default inferred from the CDL.
-x Output XML (NcML) instead of CDL. The NcML does not include data values. The NcML
output option currently only works for netCDF classic model data.
-s Output special virtual attributes that provide performance-related information
about the file format and variable properties for netCDF-4 data. These special
virtual attributes are not actually part of the data, they are merely a convenient
way to display miscellaneous properties of the data in CDL (and eventually NcML).
They include `_ChunkSizes', `_DeflateLevel', `_Endianness', `_Fletcher32',
`_Format', `_NoFill', `_Shuffle', and `_Storage'. `_ChunkSizes' is a list of chunk
sizes for each dimension of the variable. `_DeflateLevel' is an integer between 0
and 9 inclusive if compression has been specified for the variable. `_Endianness'
is either `little' or `big', depending on how the variable was stored when first
written. `_Fletcher32' is `true' if the checksum property was set for the
variable. `_Format' is a global attribute specifying the netCDF format variant,
one of `classic', `64-bit offset', `netCDF-4', or `netCDF-4 classic model'.
`_NoFill' is `true' if the persistent NoFill property was set for the variable when
it was defined. `_Shuffle' is `true' if use of the shuffle filter was specified
for the variable. `_Storage' is `contiguous' or `chunked', depending on how the
variable's data is stored.
-t Controls display of time data, if stored in a variable that uses a udunits
compliant time representation such as `days since 1970-01-01' or `seconds since
2009-03-15 12:01:17'. If this option is specified, time values are displayed as
human-readable date-time strings rather than numerical values, interpreted in terms
of a `calendar' variable attribute, if specified. Calendar attribute values
interpreted with this option include the CF Conventions values `gregorian' or
`standard', `proleptic_gregorian', `noleap' or `365_day', `all_leap' or `366_day',
`360_day', and `julian'.
EXAMPLES
Look at the structure of the data in the netCDF file `foo.nc':
ncdump -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 -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 -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':
ncdump -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. Climate and Forecast
Metadata Conventions, http://www.cfconventions.org.
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.