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<title>GRDROTATER</title>
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<h1 align="center">GRDROTATER</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="#COORDINATES">COORDINATES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<hr>
<h2>NAME
<a name="NAME"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">grdrotater
− Rotate a grid using a finite rotation</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdrotate</b>
<i>ingrdfile</i> <b>−G</b><i>outgrdfile</i>
<b>−T</b><i>plon</i>/<i>plat</i>/<i>omega</i> [
<b>−F</b><i>polygonfile</i> ] [
<b>−H</b>[<b>i</b>][<i>nrec</i>] ] [ <b>−N</b> ]
[
<b>−Q</b>[<b>b</b>|<b>c</b>|<b>l</b>|<b>n</b>][[<b>/</b>]<i>threshold</i>]
] [
<b>−R</b><i>west</i>/<i>east</i>/<i>south</i>/<i>north</i>[<b>r</b>]
] [ <b>−S</b> ] [ <b>−V</b> ] [
<b>−:</b>[<b>i</b>|<b>o</b>] ] [
<b>−b</b>[<b>i</b>|<b>o</b>][<b>s</b>|<b>S</b>|<b>d</b>|<b>D</b>[<i>ncol</i>]|<b>c</b>[<i>var1</i><b>/</b><i>...</i>]]
] [ <b>−m</b>[<i>flag</i>] ]</p>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdrotater</b>
reads a geographical grid and reconstructs it given a total
reconstruction rotation. Optionally, the user may supply a
clipping polygon in multiple-segment format; then, only the
part of the grid inside the polygon is used to determine the
return grid region. The outline of the projected region is
returned on stdout provided the rotated region is not the
entire globe.</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
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<td width="8%"></td>
<td width="7%"></td>
<td width="85%">
<p>No space between the option flag and the associated
arguments. Use upper case for the option flags and lower
case for modifiers.</p></td></tr>
</table>
<p style="margin-left:11%;"><i>ingrdfile</i></p>
<p style="margin-left:22%;">Name of a grid file in
geographical (lon, lat) coordinates.</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>−G</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>Name of output grid. This is the grid with the data
reconstructed according to the specified rotation.</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>Finite rotation. Specify the longitude and latitude of
the rotation pole and the opening angle, all in degrees.</p></td></tr>
</table>
<h2>OPTIONS
<a name="OPTIONS"></a>
</h2>
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cellspacing="0" cellpadding="0">
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<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em"><b>−F</b></p></td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em">Specify a multi-segment closed
polygon file that describes the inside area of the grid that
should be projected [Default projects entire grid].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−H</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Input file(s) has header record(s). If used, the default
number of header records is <b><A HREF="gmtdefaults.html#N_HEADER_RECS">N_HEADER_RECS</A></b>. Use
<b>−Hi</b> if only input data should have header
records [Default will write out header records if the input
data have them]. Blank lines and lines starting with # are
always skipped.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−N</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Do Not output the rotated polygon outline [Default will
write it to stdout].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−Q</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Quick mode, use bilinear rather than bicubic
interpolation [Default]. Alternatively, select the
interpolation mode by adding <b>b</b> for B-spline
smoothing, <b>c</b> for bicubic interpolation, <b>l</b> for
bilinear interpolation or <b>n</b> for nearest-neighbor
value. Optionally, append <i>threshold</i> in the range
[0,1]. This parameter controls how close to nodes with NaN
values the interpolation will go. E.g., a <i>threshold</i>
of 0.5 will interpolate about half way from a non-NaN to a
NaN node, whereas 0.1 will go about 90% of the way, etc.
[Default is 1, which means none of the (4 or 16) nearby
nodes may be NaN]. <b>−Q0</b> will just return the
value of the nearest node instead of interpolating. This is
the same as using <b>−Qn</b>.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−R</b></p></td>
<td width="7%"></td>
<td width="78%">
<p><i>west, east, south,</i> and <i>north</i> specify the
Region of interest, 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.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−S</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Skip the rotation of the grid, just rotate the polygon
outline (requires <b>−F</b>).</p></td></tr>
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<td width="11%"></td>
<td width="4%">
<p><b>−V</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Selects verbose mode, which will send progress reports
to stderr [Default runs "silently"].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−:</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Toggles between (longitude,latitude) and
(latitude,longitude) input/output. [Default is
(longitude,latitude)].</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−bi</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Selects binary input. Append <b>s</b> for single
precision [Default is <b>d</b> (double)]. Uppercase <b>S</b>
or <b>D</b> will force byte-swapping. Optionally, append
<i>ncol</i>, the number of columns in your binary input file
if it exceeds the columns needed by the program. Or append
<b>c</b> if the input file is netCDF. Optionally, append
<i>var1</i><b>/</b><i>var2</i><b>/</b><i>...</i> to specify
the variables to be read. [Default is 2 input columns].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−bo</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Selects binary output. Append <b>s</b> for single
precision [Default is <b>d</b> (double)]. Uppercase <b>S</b>
or <b>D</b> will force byte-swapping. Optionally, append
<i>ncol</i>, the number of desired columns in your binary
output file. [Default is same as input].</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−m</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Multiple segment file(s). Segments are separated by a
special record. For ASCII files the first character must be
<i>flag</i> [Default is ’>’]. For binary
files all fields must be NaN and <b>−b</b> must set
the number of output columns explicitly. By default the
<b>−m</b> setting applies to both input and output.
Use <b>−mi</b> and <b>−mo</b> to give separate
settings to input and output.</p></td></tr>
</table>
<h2>EXAMPLES
<a name="EXAMPLES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">To rotate the
data defined by grid topo.grd and the polygon outline
clip_path.d, using a finite rotation with pole at (135.5,
-33.0) and a rotation angle of 37.3 degrees and bicubic
interpolation, try</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdrotater</b>
topo.grd <b>−T</b> 135.5/-33/37.3 <b>−V
−F</b> clip_path.d <b>−G</b> rot_topo.grd >
rot_clip_path.d</p>
<p style="margin-left:11%; margin-top: 1em">To rotate the
entire grid faa.grd using a finite rotation pole at (67:45W,
22:35S) and a rotation angle of 19.6 degrees using a
bilinear interpolation, try</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdrotater</b>
faa.grd <b>−T</b> 67:45W/22:35S/19.6 <b>−V
−Q −G</b> rot_faa.grd > rot_faa_path.d</p>
<p style="margin-left:11%; margin-top: 1em">To just see how
the outline of the grid large.grd will plot after the same
rotation, try</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdrotater</b>
large.grd <b>−T</b> 67:45W/22:35S/19.6 <b>−V
−S</b> | psxy <b>−Rg −JH</b> 180/6i
<b>−B</b> 30 <b>−m −W</b> 0.5<b>p</b> | gv
-</p>
<p style="margin-left:11%; margin-top: 1em">Let say you
have rotated gridA.grd and gridB.grd, restricting each
rotation to nodes inside polygons polyA.d and polyB.d,
respectively, using rotation A = (123W,22S,16,4) and
rotation B = (108W, 16S, -14.5), yielding rotated grids
rot_gridA.grd and rot_gridB.grd. To determine the region of
overlap between the rotated grids, we use grdmath:</p>
<p style="margin-left:11%; margin-top: 1em">grdmath 1
rot_gridA.grd ISNAN SUB 1 rot_gridB.grd ISNAN SUB 2 EQ =
overlap.grd</p>
<p style="margin-left:11%; margin-top: 1em">The grid
overlap.grd now has 1s in the regions of overlap and 0
elsewhere. You can use it as a mask or use grdcontour to
extract a polygon (contour).</p>
<h2>COORDINATES
<a name="COORDINATES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">Data
coordinates are assumed to be geodetic and will
automatically be converted to geocentric before spherical
rotations are performed. We convert back to geodetic
coordinates for output. Note: If your data already are
geocentric, you can avoid the conversion by using
--ELLIPSOID=sphere.</p>
<h2>SEE ALSO
<a name="SEE ALSO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><i><A HREF="backtracker.html">backtracker</A></i>(1),
<i><A HREF="grdspotter.html">grdspotter</A></i>(1), <i><A HREF="hotspotter.html">hotspotter</A></i>(1),
<i><A HREF="originator.html">originator</A></i>(1) <i><A HREF="rotconverter.html">rotconverter</A></i>(1)</p>
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