NCMPIDUMP(1) UTILITIES NCMPIDUMP(1)NAMEncmpidump - Convert netCDF files to ASCII form (CDL)
SYNOPSISncmpidump [-ch] [-v var1,...] [-b lang] [-f lang] [-l len] [-n name]
[-p f_digits[,d_digits]] file
ncmpidump-k file
DESCRIPTIONncmpidump 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 ncmpigen. ncmpigen is a companion program that can
generate a binary netCDF file from a CDL file. Hence ncmpigen and
ncmpidump can be used as inverses to transform the data representation
between binary and ASCII representations. See ncmpigen for a descrip‐
tion of CDL and netCDF representations.
ncmpidump may also be used to determine what kind of netCDF file is
used (which variant of the netCDF file format) with the -k option.
ncmpidump 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' at‐
tribute to format each value. For example, if floating-point data for
the netCDF variable `Z' is known to be accurate to only three signifi‐
cant digits, it would be appropriate to use the variable attribute
Z:C_format = "%.3g"
ncmpidump 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.
ncmpidump 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.
OPTIONS-c Show the values of coordinate variables (variables that are also
dimensions) as well as the declarations of all dimensions, vari‐
ables, 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 dec‐
larations 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 val‐
ues for multidimensional variables. If lang begins with `C' or
`c', then C language conventions will be used (zero-based in‐
dices, 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 an‐
notations 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 be‐
ginning 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 lan‐
guage conventions will be used (zero-based indices, last dimen‐
sion 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 dif‐
fer. This option may be useful for piping data into other fil‐
ters, 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. Al‐
though the output file name used by ncmpigen -b can be speci‐
fied, 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 over‐
rides the value of the `C_format' attribute for any variable
that has such an attribute. Floating-point data will be dis‐
played 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 speci‐
fied, 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 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 an‐
other variant of the format, designated as `64-bit data' (known
as format variant 5 or CDF-5).
EXAMPLES
Look at the structure of the data in the netCDF file `foo.nc':
ncmpidump-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:
ncmpidump-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 signif‐
icant 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':
ncmpidump-v omega -f fortran -n omega foo.nc > Z.cdl
REFERENCES
What Every Computer Scientist should Know About Floating-Point Arith‐
metic, D. Goldberg, ACM Computing Surveys, Vol. 23, No. 1, March 1991,
pp. 5-48.
SEE ALSOncmpigen(1), pnetcdf(3)DATE
$Date: 2013-11-17 00:21:28 -0600 (Sun, 17 Nov 2013) $
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 short‐
er 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: 2024-04-29 2013-11-17 NCMPIDUMP(1)
