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

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, 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-
       hdf 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-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 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. 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 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-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 ncdump-
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 precision 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_format'
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 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 -d 9,17 (according to Theorem 15 of the paper listed
under REFERENCES).

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 indexing 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 floating-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.