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<title>GRDREFORMAT</title>
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<h1 align=center>GRDREFORMAT</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="#FORMAT IDENTIFIER">FORMAT IDENTIFIER</a><br>
<a href="#GMT STANDARD NETCDF FILES">GMT STANDARD NETCDF FILES</a><br>
<a href="#NATIVE BINARY FILES">NATIVE BINARY FILES</a><br>
<a href="#GRID VALUES PRECISION">GRID VALUES PRECISION</a><br>
<a href="#EXAMPLES">EXAMPLES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<hr>
<a name="NAME"></a>
<h2>NAME</h2>
<p style="margin-left:11%; margin-top: 1em">grdreformat
− Converting between different grid file formats.</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdreformat</b>
<i>ingrdfile</i>[<i>=id</i>[<i>/scale/offset</i>[<i>/NaNvalue</i>]]]
<i>outgrdfile</i>[<i>=id</i>[<i>/scale/offset</i>[<i>/NaNvalue</i>]]]
[ <b>−N</b> ] [
<b>−R</b><i>west</i>/<i>east</i>/<i>south</i>/<i>north</i>[<b>r</b>]
] [ <b>−f</b>[<b>i</b>|<b>o</b>]<i>colinfo</i> ] [
<b>−V</b> ]</p>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdreformat</b>
reads a grid file in one format and writes it out using
another format. As an option the user may select a subset of
the data to be written and to specify scaling, translation,
and NaN-value. <i><br>
ingrdfile</i></p>
<p style="margin-left:22%;">The grid file to be read.
Append format =<i>id</i> code if not a standard
COARDS-compliant netCDF grid file. If =<i>id</i> is set (see
below), you may optionally append <i>scale</i> and
<i>offset</i>. These options will scale the data and then
offset them with the specified amounts after reading. <br>
If <i>scale</i> and <i>offset</i> are supplied you may also
append a value that represents ’Not-a-Number’
(for floating-point grids this is unnecessary since the IEEE
NaN is used; however integers need a value which means no
data available.)</p>
<p style="margin-left:11%;"><i>outgrdfile</i></p>
<p style="margin-left:22%;">The grid file to be written.
Append format =<i>id</i> code if not a standard
COARDS-compliant netCDF grid file. If =<i>id</i> is set (see
below), you may optionally append <i>scale</i> and
<i>offset</i>. These options are particularly practical when
storing the data as integers, first removing an offset and
then scaling down the values. Since the scale and offset are
applied in reverse order when reading, this does not affect
the data values (except for round-offs). <br>
If <i>scale</i> and <i>offset</i> are supplied you may also
append a value that represents ’Not-a-Number’
(for floating-point grids this is unnecessary since the IEEE
NaN is used; however integers need a value which means no
data available.)</p>
<a name="OPTIONS"></a>
<h2>OPTIONS</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="3%">
<p style="margin-top: 1em" valign="top"><b>−N</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Suppress the
writing of the <b><A HREF="GMT.html">GMT</A></b> header structure. This is useful
when you want to write a native grid to be used by
<b><A HREF="grdraster.html">grdraster</A></b>. It only applies to native grids and is
ignored for netCDF output.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−R</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top"><i>xmin</i>,
<i>xmax</i>, <i>ymin</i>, and <i>ymax</i> specify the Region
of interest. For geographic regions, these limits correspond
to <i>west, east, south,</i> and <i>north</i> and you may
specify them in decimal degrees or in
[+-]dd:mm[:ss.xxx][W|E|S|N] format. Append <b>r</b> if lower
left and upper right map coordinates are given instead of
w/e/s/n. The two shorthands <b>−Rg</b> and
<b>−Rd</b> stand for global domain (0/360 and
-180/+180 in longitude respectively, with -90/+90 in
latitude). Alternatively, specify the name of an existing
grid file and the <b>−R</b> settings (and grid
spacing, if applicable) are copied from the grid. For
calendar time coordinates you may either give (a) relative
time (relative to the selected <b><A HREF="gmtdefaults.html#TIME_EPOCH">TIME_EPOCH</A></b> and in the
selected <b><A HREF="gmtdefaults.html#TIME_UNIT">TIME_UNIT</A></b>; append <b>t</b> to
<b>−JX</b>|<b>x</b>), or (b) absolute time of the form
[<i>date</i>]<b>T</b>[<i>clock</i>] (append <b>T</b> to
<b>−JX</b>|<b>x</b>). At least one of <i>date</i> and
<i>clock</i> must be present; the <b>T</b> is always
required. The <i>date</i> string must be of the form
[-]yyyy[-mm[-dd]] (Gregorian calendar) or yyyy[-Www[-d]]
(ISO week calendar), while the <i>clock</i> string must be
of the form hh:mm:ss[.xxx]. The use of delimiters and their
type and positions must be exactly as indicated (however,
input, output and plot formats are customizable; see
<b><A HREF="gmtdefaults.html">gmtdefaults</A></b>).</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−V</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects verbose
mode, which will send progress reports to stderr [Default
runs "silently"].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−f</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Special formatting
of input and/or output columns (time or geographical data).
Specify <b>i</b> or <b>o</b> to make this apply only to
input or output [Default applies to both]. Give one or more
columns (or column ranges) separated by commas. Append
<b>T</b> (absolute calendar time), <b>t</b> (relative time
in chosen <b><A HREF="gmtdefaults.html#TIME_UNIT">TIME_UNIT</A></b> since <b><A HREF="gmtdefaults.html#TIME_EPOCH">TIME_EPOCH</A></b>),
<b>x</b> (longitude), <b>y</b> (latitude), or <b>f</b>
(floating point) to each column or column range item.
Shorthand <b>−f</b>[<b>i</b>|<b>o</b>]<b>g</b> means
<b>−f</b>[<b>i</b>|<b>o</b>]0<b>x</b>,1<b>y</b>
(geographic coordinates).</p></td>
</table>
<a name="FORMAT IDENTIFIER"></a>
<h2>FORMAT IDENTIFIER</h2>
<p style="margin-left:11%; margin-top: 1em">By default,
grids will be written as floating point data stored in
binary files using the netCDF format and meta-data
structure. This format is conform the COARDS conventions.
<b><A HREF="GMT.html">GMT</A></b> versions prior to 4.1 produced netCDF files that
did not conform to these conventions. Although these files
are still supported, their use is deprecated. To write other
than floating point COARDS-compliant netCDF files, append
the =<i>id</i> suffix to the filename <i>outgrdfile</i>.
<br>
When reading files, <b>grdreformat</b> and other <b><A HREF="GMT.html">GMT</A></b>
programs will automatically recognize any type of netCDF
grid file. These can be in either COARDS-compliant or
pre-4.1 format, and contain floating-point or integer data.
To read other types of grid files, append the =<i>id</i>
suffix to the filename <i>ingrdfile</i>.</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%"></td>
<td width="7%">
<p valign="top"><i>id</i></p></td>
<td width="85%">
<p valign="top"><i>GMT 3 netCDF legacy formats</i></p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>cb</b></p></td>
<td width="85%">
<p valign="top">GMT netCDF format (byte) (deprecated)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>cs</b></p></td>
<td width="85%">
<p valign="top">GMT netCDF format (short) (deprecated)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>ci</b></p></td>
<td width="85%">
<p valign="top">GMT netCDF format (int) (deprecated)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>cf</b></p></td>
<td width="85%">
<p valign="top">GMT netCDF format (float) (deprecated)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>cd</b></p></td>
<td width="85%">
<p valign="top">GMT netCDF format (double) (deprecated)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><i>id</i></p></td>
<td width="85%">
<p valign="top"><i>GMT native binary formats</i></p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>bm</b></p></td>
<td width="85%">
<p valign="top">GMT native, C-binary format (bit-mask)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>bb</b></p></td>
<td width="85%">
<p valign="top">GMT native, C-binary format (byte)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>bs</b></p></td>
<td width="85%">
<p valign="top">GMT native, C-binary format (short)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>bi</b></p></td>
<td width="85%">
<p valign="top">GMT native, C-binary format (int)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>bf</b></p></td>
<td width="85%">
<p valign="top">GMT native, C-binary format (float)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>bd</b></p></td>
<td width="85%">
<p valign="top">GMT native, C-binary format (double)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><i>id</i></p></td>
<td width="85%">
<p valign="top"><i>GMT 4 netCDF standard</i></p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>nb</b></p></td>
<td width="85%">
<p valign="top">GMT netCDF format (byte)
(COARDS-compliant)</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>ns</b></p></td>
<td width="85%">
<p valign="top">GMT netCDF format (short)
(COARDS-compliant)</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>ni</b></p></td>
<td width="85%">
<p valign="top">GMT netCDF format (int)
(COARDS-compliant)</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>nf</b></p></td>
<td width="85%">
<p valign="top">GMT netCDF format (float)
(COARDS-compliant) [DEFAULT]</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>nd</b></p></td>
<td width="85%">
<p valign="top">GMT netCDF format (double)
(COARDS-compliant)</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><i>id</i></p></td>
<td width="85%">
<p valign="top"><i>Misc formats</i></p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>rb</b></p></td>
<td width="85%">
<p valign="top">SUN rasterfile format (8-bit standard)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>rf</b></p></td>
<td width="85%">
<p valign="top">GEODAS grid format GRD98 (NGDC)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>sf</b></p></td>
<td width="85%">
<p valign="top">Golden Software Surfer format 6 (float)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>sd</b></p></td>
<td width="85%">
<p valign="top">Golden Software Surfer format 7 (double,
read-only)</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>af</b></p></td>
<td width="85%">
<p valign="top">Atlantic Geoscience Center format AGC
(float)</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="7%">
<p valign="top"><b>gd</b></p></td>
<td width="85%">
<p valign="top">Import through GDAL (convert to float) --
NON-STANDARD</p> </td>
</table>
<a name="GMT STANDARD NETCDF FILES"></a>
<h2>GMT STANDARD NETCDF FILES</h2>
<p style="margin-left:11%; margin-top: 1em">The standard
format used for gdrfiles is based on netCDF and conforms to
the COARDS conventions. Files written in this format can be
read by numerous third-party programs and are
platform-independent. Some disk-space can be saved by
storing the data as bytes or shorts in stead of integers.
Use the <i>scale</i> and <i>offset</i> parameters to make
this work without loss of data range or significance. For
more details, see Appendix B.</p>
<p style="margin-left:11%; margin-top: 1em"><b>Multi-variable
grid files</b> <br>
By default, <b><A HREF="GMT.html">GMT</A></b> programs will read the first
2-dimensional grid contained in a COARDS-compliant netCDF
file. Alternatively, use
<i>ingrdfile</i><b>?</b><i>varname</i> (ahead of any
optional suffix <b>=</b><i>id</i>) to specify the requested
variable <i>varname</i>. Since <b>?</b> has special meaning
as a wildcard, escape this meaning by placing the full
filename and suffix between quotes.</p>
<p style="margin-left:11%; margin-top: 1em"><b>Multi-dimensional
grids</b> <br>
To extract one <i>layer</i> or <i>level</i> from a
3-dimensional grid stored in a COARDS-compliant netCDF file,
append both the name of the variable and the index
associated with the layer (starting at zero) in the form:
<i>ingrdfile</i><b>?</b><i>varname</i><b>[</b><i>layer</i><b>]</b>.
Alternatively, specify the value associated with that layer
using parentheses in stead of brackets:
<i>ingridfile</i><b>?</b><i>varname</i><b>(</b><i>level</i><b>)</b>.
<br>
In a similar way layers can be extracted from 4- or even
5-dimensional grids. For example, if a grid has the
dimensions (parameter, time, depth, latitude, longitude), a
map can be selected by using:
<i>ingridfile</i><b>?</b><i>varname</i><b>(</b><i>parameter,time,depth</i><b>)</b>.
<br>
Since question marks, brackets and parentheses have special
meanings on the command line, escape these meanings by
placing the full filename and suffix between quotes.</p>
<a name="NATIVE BINARY FILES"></a>
<h2>NATIVE BINARY FILES</h2>
<p style="margin-left:11%; margin-top: 1em">For binary
native <b><A HREF="GMT.html">GMT</A></b> files the size of the <b><A HREF="GMT.html">GMT</A></b> grdheader
block is <i>hsize</i> = 892 bytes, and the total size of the
file is <i>hsize</i> + <i>nx</i> * <i>ny</i> *
<i>item_size</i>, where <i>item_size</i> is the size in
bytes of each element (1, 2, 4). Bit grids are stored using
4-byte integers, each holding 32 bits, so for these files
the size equation is modified by using ceil (<i>nx</i> / 32)
* 4 instead of <i>nx</i>. Note that these files are
platform-dependent. Files written on Little Endian machines
(e.g. PCs) can not be read on Big Endian machines (e.g. most
workstations). Also note that it is not possible for
<b><A HREF="GMT.html">GMT</A></b> to determine uniquely if a 4-byte grid is float
or int; in such cases it is best to use the <i>=ID</i>
mechanism to specify the file format. For header and grid
details, see Appendix B.</p>
<a name="GRID VALUES PRECISION"></a>
<h2>GRID VALUES PRECISION</h2>
<p style="margin-left:11%; margin-top: 1em">Regardless of
the precision of the input data, GMT programs that create
grid files will internally hold the grids in 4-byte floating
point arrays. This is done to conserve memory and
furthermore most if not all real data can be stored using
4-byte floating point values. Data with higher precision
(i.e., double precision values) will lose that precision
once GMT operates on the grid or writes out new grids. To
limit loss of precision when processing data you should
always consider normalizing the data prior to
processing.</p>
<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
<p style="margin-left:11%; margin-top: 1em">To extract the
second layer from a 3-dimensional grid named temp from a
COARDS-compliant netCDF file climate.grd:</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdreformat</b>
climate.grd?temp[1] temp.grd <b>-V</b></p>
<p style="margin-left:11%; margin-top: 1em">To create a
4-byte native floating point grid from the COARDS-compliant
netCDF file data.grd:</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdreformat</b>
data.grd ras_data.b4=bf <b>−V</b></p>
<p style="margin-left:11%; margin-top: 1em">To make a
2-byte short integer file, scale it by 10, subtract 32000,
setting NaNs to -9999, do</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdreformat</b>
values.grd shorts.i2=bs/10/-32000/-9999 <b>−V</b></p>
<p style="margin-left:11%; margin-top: 1em">To create a Sun
standard 8-bit rasterfile for a subset of the data file
image.grd, assuming the range in image.grd is 0-1 and we
need 0-255, run</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdreformat</b>
image.grd <b>−R</b>-60/-40/-40/-30 image.ras8=rb/255/0
<b>−V</b></p>
<p style="margin-left:11%; margin-top: 1em">To convert
etopo2.grd to etopo2.i2 that can be used by
<b><A HREF="grdraster.html">grdraster</A></b>, try</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdreformat</b>
etopo2.grd etopo2.i2=bs <b>−N −V</b></p>
<a name="SEE ALSO"></a>
<h2>SEE ALSO</h2>
<p style="margin-left:11%; margin-top: 1em"><i><A HREF="GMT.html">GMT</A></i>(1),
<i><A HREF="grdmath.html">grdmath</A></i>(1)</p>
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