NCDUMP(1) UNIDATA UTILITIES NCDUMP(1)NAMEncdump - Convert netCDF files to ASCII form (CDL)
SYNOPSISncdump [-c] [-h] [-v var1,...] [-b lang] [-f lang] [-l len] [-n name]
[-d f_digits[,d_digits]] file
DESCRIPTIONncdump 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 gener‐
ate 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 ASCII representations. See ncgen for a description of CDL and
netCDF representations.
ncdump 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 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.
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 ncgen -b
in generating a default netCDF file name. By default, ncdump
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 change the default name to avoid inadver‐
tantly 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.
-d float_digits[,double_digits]
Specifies default number of significant digits to use in dis‐
playing floating-point or double precision data values for vari‐
ables 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, float‐
ing-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 dou‐
ble-presision precisions are specified, the two values must ap‐
pear 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 possi‐
ble floating-point values, you will have to specify this with -d
9,17 (according to Theorem 15 of the paper listed under REFER‐
ENCES).
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 signif‐
icant digits of precision:
ncdump-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-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 ALSOncgen(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 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: 124-4-18 1996-03-26 NCDUMP(1)
