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<title>NCDUMP</title>
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<h1 align="center">NCDUMP</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#OPTIONS">OPTIONS</a><br>
<a href="#EXAMPLES">EXAMPLES</a><br>
<a href="#REFERENCES">REFERENCES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#BUGS">BUGS</a><br>
<hr>
<h2>NAME
<a name="NAME"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">ncdump −
Convert netCDF file to text form (CDL)</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="89%">
<p style="margin-top: 1em">ncdump [-c] [-h] [-v
<i>var1,...</i>] [-b <i>lang</i>] [-f <i>lang</i>] [-l
<i>len</i>] [-n <i>name</i>] [-p <i>f_digits[,d_digits]</i>]
[-k] [-x] [-s] [-t] <i>file</i></p></td></tr>
</table>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><i><b>ncdump</b></i>
generates a text representation of a specified netCDF file
on standard output. The text representation is in a form
called CDL (‘‘network Common Data form
Language’’) that can be viewed, edited, or serve
as input to <b>ncgen</b>. <b>ncgen</b> is a companion
program that can generate a binary netCDF file from a CDL
file. Hence <b>ncgen</b> and <b>ncdump</b> can be used as
inverses to transform the data representation between binary
and text representations. See <b>ncgen</b> for a description
of CDL and netCDF representations.</p>
<p style="margin-left:11%; margin-top: 1em">As of NetCDF
version 4.1, and if DAP support was enabled when
<b>ncdump</b> was built, the file name may specify a DAP
URL. This allows <b>ncdump</b> to print out data sources
from DAP servers. When used with the <b>-h</b> option,
<b>ncdump</b> can be used to show the translation from the
DAP DDS data model to the NetCDF data model.</p>
<p style="margin-left:11%; margin-top: 1em"><b>ncdump</b>
defines a default display 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, <b>ncdump</b> 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</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="22%"></td>
<td width="29%">
<p style="margin-top: 1em">Z:C_format =
"%.3g"</p> </td>
<td width="49%">
</td></tr>
</table>
<p style="margin-left:11%; margin-top: 1em"><b>ncdump</b>
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.</p>
<p style="margin-left:11%; margin-top: 1em"><b>ncdump</b>
uses ‘_’ to represent data values that are equal
to the ‘_FillValue’ attribute for a variable,
intended to represent data that has not yet been written. If
a variable has no ‘_FillValue’ attribute, the
default fill value for the variable type is used if the
variable is not of byte type.</p>
<p style="margin-left:11%; margin-top: 1em"><b>ncdump</b>
may also be used to determine what kind of netCDF file is
used (which variant of the netCDF file format) with the -k
option.</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<h2>OPTIONS
<a name="OPTIONS"></a>
</h2>
<td width="11%"></td>
<td width="3%"></td>
<td width="8%"></td>
<td width="78%">
</td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>-c</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Show the values of <i>coordinate</i> 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.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>-h</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Show only the <i>header</i> 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 <b>-c</b> option except that the
values of coordinate variables are not included. (At most
one of <b>-c</b> or <b>-h</b> options may be present.)</p></td></tr>
</table>
<p style="margin-left:11%;"><b>-v</b>
<i>var1,...,varn</i></p>
<p style="margin-left:22%;">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 unless escaped. The
named variables must be valid netCDF variables in the
input-file. A variable within a group in a netCDF-4 file may
be specified with an absolute path name, such as
‘/GroupA/GroupA2/var’. Use of a relative path
name such as ‘var’ or ‘grp/var’
specifies all matching variable names in the file. The
default, without this option and in the absence of the
<b>-c</b> or <b>-h</b> options, is to include data values
for <i>all</i> variables in the output.</p>
<p style="margin-left:11%;"><b>-b</b> <i>lang</i></p>
<p style="margin-left:22%;">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
<i>lang</i> begins with ‘C’ or ‘c’,
then C language conventions will be used (zero-based
indices, last dimension varying fastest). If <i>lang</i>
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.</p>
<p style="margin-left:11%;"><b>-f</b> <i>lang</i></p>
<p style="margin-left:22%;">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 <i>lang</i> begins with
‘C’ or ‘c’, then C language
conventions will be used (zero-based indices, last dimension
varying fastest). If <i>lang</i> 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.</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p><b>-l</b> <i>len</i></p></td>
<td width="2%"></td>
<td width="78%">
<p>Changes the default maximum line length (80) used in
formatting lists of non-character data values.</p></td></tr>
</table>
<p style="margin-left:11%;"><b>-n</b> <i>name</i></p>
<p style="margin-left:22%;">CDL requires a name for a
netCDF data set, for use by <b>ncgen -b</b> in generating a
default netCDF file name. By default, <i>ncdump</i>
constructs this name from the last component of the path
name of the input netCDF file by stripping off any extension
it has. Use the <b>-n</b> option to specify a different
name. Although the output file name used by <b>ncgen -b</b>
can be specified, it may be wise to have <i>ncdump</i>
change the default name to avoid inadvertently overwriting a
valuable netCDF file when using <b>ncdump</b>, editing the
resulting CDL file, and using <b>ncgen -b</b> to generate a
new netCDF file from the edited CDL file.</p>
<p style="margin-left:11%;"><b>-p</b>
<i>float_digits[,double_digits]</i></p>
<p style="margin-left:22%;">Specifies default precision
(number of significant digits) to use in displaying
floating-point or double precision data values for
attributes and variables. If specified, this value overrides
the value of the ‘C_format’ attribute for any
variable that has such an attribute. Floating-point data
will be displayed with <i>float_digits</i> significant
digits. If <i>double_digits</i> is also specified,
double-precision values will be displayed with that many
significant digits. In the absence of any <b>-p</b>
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-precision 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 <b>-p 9,17</b>
(according to Theorem 15 of the paper listed under
REFERENCES).</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>-k</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Show what kind of netCDF file the pathname references,
one of ‘classic’, ‘64-bit
offset’,‘netCDF-4’, or ‘netCDF-4
classic model’. Before version 3.6, there was only one
kind of netCDF file, designated as ‘classic’
(also know as format variant 1). Large file support
introduced another variant of the format, designated as
‘64-bit offset’ (known as format variant 2).
NetCDF-4, uses a third variant of the format,
‘netCDF-4’ (format variant 3). Another format
variant, designated ‘netCDF-4 classic model’
(format variant 4), is restricted to features supported by
the netCDF-3 data model but represented using the HDF5
format, so that an unmodified netCDF-3 program can read or
write the file just by relinking with the netCDF-4 library.
The string output by using the ‘-k’ option may
be provided as the value of the ‘-k’ option to
ncgen(1) to specify exactly what kind of netCDF file to
generate, when you want to override the default inferred
from the CDL.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>-x</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Output XML (NcML) instead of CDL. The NcML does not
include data values. The NcML output option currently only
works for netCDF classic model data.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>-s</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Output special virtual attributes that provide
performance-related information about the file format and
variable properties for netCDF-4 data. These special virtual
attributes are not actually part of the data, they are
merely a convenient way to display miscellaneous properties
of the data in CDL (and eventually NcML). They include
‘_ChunkSizes’, ‘_DeflateLevel’,
‘_Endianness’, ‘_Fletcher32’,
‘_Format’, ‘_NoFill’,
‘_Shuffle’, and ‘_Storage’.
‘_ChunkSizes’ is a list of chunk sizes for each
dimension of the variable. ‘_DeflateLevel’ is an
integer between 0 and 9 inclusive if compression has been
specified for the variable. ‘_Endianness’ is
either ‘little’ or ‘big’, depending
on how the variable was stored when first written.
‘_Fletcher32’ is ‘true’ if the
checksum property was set for the variable.
‘_Format’ is a global attribute specifying the
netCDF format variant, one of ‘classic’,
‘64-bit offset’, ‘netCDF-4’, or
‘netCDF-4 classic model’. ‘_NoFill’
is ‘true’ if the persistent NoFill property was
set for the variable when it was defined.
‘_Shuffle’ is ‘true’ if use of the
shuffle filter was specified for the variable.
‘_Storage’ is ‘contiguous’ or
‘chunked’, depending on how the variable’s
data is stored.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p><b>-t</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Controls display of time data, if stored in a variable
that uses a udunits compliant time representation such as
‘days since 1970-01-01’ or ‘seconds since
2009-03-15 12:01:17’. If this option is specified,
time values are displayed as human-readable date-time
strings rather than numerical values, interpreted in terms
of a ‘calendar’ variable attribute, if
specified. Calendar attribute values interpreted with this
option include the CF Conventions values
‘gregorian’ or ‘standard’,
‘proleptic_gregorian’, ‘noleap’ or
‘365_day’, ‘all_leap’ or
‘366_day’, ‘360_day’, and
‘julian’.</p> </td></tr>
</table>
<h2>EXAMPLES
<a name="EXAMPLES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">Look at the
structure of the data in the netCDF file
‘<b>foo.nc</b>’:</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="22%"></td>
<td width="24%">
<p style="margin-top: 1em">ncdump -c foo.nc</p></td>
<td width="54%">
</td></tr>
</table>
<p style="margin-left:11%; margin-top: 1em">Produce an
annotated CDL version of the structure and data in the
netCDF file ‘<b>foo.nc</b>’, using C-style
indexing for the annotations:</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="22%"></td>
<td width="43%">
<p style="margin-top: 1em">ncdump -b c foo.nc >
foo.cdl</p> </td>
<td width="35%">
</td></tr>
</table>
<p style="margin-left:11%; margin-top: 1em">Output data for
only the variables ‘uwind’ and
‘vwind’ from the netCDF file
‘<b>foo.nc</b>’, and show the floating-point
data with only three significant digits of precision:</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="22%"></td>
<td width="50%">
<p style="margin-top: 1em">ncdump -v uwind,vwind -p 3
foo.nc</p> </td>
<td width="28%">
</td></tr>
</table>
<p style="margin-left:11%; margin-top: 1em">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’:</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="22%"></td>
<td width="76%">
<p style="margin-top: 1em">ncdump -v omega -f fortran -n
omega foo.nc > Z.cdl</p></td>
<td width="2%">
</td></tr>
</table>
<h2>REFERENCES
<a name="REFERENCES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><i>What Every
Computer Scientist should Know About Floating-Point
Arithmetic</i>, D. Goldberg, <b>ACM Computing Surveys, Vol.
23, No. 1</b>, March 1991, pp. 5-48. Climate and Forecast
Metadata Conventions, http://www.cfconventions.org.</p>
<h2>SEE ALSO
<a name="SEE ALSO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>ncgen</b>(1),
<b>netcdf</b>(3)</p>
<h2>BUGS
<a name="BUGS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">Character
arrays that contain a null-byte are treated like C strings,
so no characters after the null byte appear in the
output.</p>
<p style="margin-left:11%; margin-top: 1em">Multidimensional
character string arrays are not handled well, since the CDL
syntax for breaking a long character string into several
shorter lines is weak.</p>
<p style="margin-left:11%; margin-top: 1em">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.</p>
<hr>
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