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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.

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.