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NCDUMP(1)		       UNIDATA UTILITIES		     NCDUMP(1)

NAME
       ncdump - Convert netCDF files to ASCII form (CDL)

SYNOPSIS
       ncdump  [-c] [-h] [-v var1,...]	[-b lang] [-f lang] [-l len] [-n name]
	      [-d f_digits[,d_digits]] file

DESCRIPTION
       ncdump 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 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 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: 121-9-17		  1996-03-26			     NCDUMP(1)
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