Ubuntu Manpage: ncdump-hdf - Convert netCDF files to ASCII form (CDL)

Provided by: hdf4-tools_4.2.16-4build1_amd64

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,  edit‐
       ed, 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 be‐
       tween 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 decla‐
rations of all dimensions, variables, and attribute values. Data values of non-coordinate vari‐
ables 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 op‐
tion 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 com‐
mand, 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 lan‐
guage 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 val‐
ues.

-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 nc‐
dump-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 pre‐
cision 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_for‐
mat' 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 float‐
ing-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 pre‐
cision 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 REF‐
ERENCES).

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 in‐
       dexing 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 float‐
       ing-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.

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: 125-7-18                                    $Date$                                            NCDUMP(1)