/usr/share/doc/gmt/html/man/grdtrend.html is in gmt-doc 4.5.11-1build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 | <!-- Creator : groff version 1.19.2 -->
<!-- CreationDate: Tue Nov 5 09:45:27 2013 -->
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta name="generator" content="groff -Thtml, see www.gnu.org">
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<meta name="Content-Style" content="text/css">
<style type="text/css">
p { margin-top: 0; margin-bottom: 0; }
pre { margin-top: 0; margin-bottom: 0; }
table { margin-top: 0; margin-bottom: 0; }
</style>
<title>GRDTREND</title>
</head>
<body bgcolor="#ffffff">
<h1 align=center>GRDTREND</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="#REMARKS">REMARKS</a><br>
<a href="#GRID FILE FORMATS">GRID FILE FORMATS</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">grdtrend
− Fit and/or remove a polynomial trend in a grid
file</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdtrend</b>
<i>grdfile</i> <b>−N</b><i>n_model</i>[<b>r</b>] [
<b>−D</b><i>diff.grd</i> ] [
<b>−T</b><i>trend.grd</i> ] [ <b>−V</b> ] [
<b>−W</b><i>weight.grd</i> ]</p>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>grdtrend</b>
reads a 2-D grid file and fits a low-order polynomial trend
to these data by [optionally weighted] least-squares. The
trend surface is defined by:</p>
<p style="margin-left:11%; margin-top: 1em">m1 + m2*x +
m3*y + m4*x*y + m5*x*x + m6*y*y + m7*x*x*x + m8*x*x*y +
m9*x*y*y + m10*y*y*y.</p>
<p style="margin-left:11%; margin-top: 1em">The user must
specify <b>−N</b><i>n_model</i>, the number of model
parameters to use; thus, <b>−N</b><i>4</i> fits a
bilinear trend, <b>−N</b><i>6</i> a quadratic surface,
and so on. Optionally, append <b>r</b> to the
<b>−N</b> option to perform a robust fit. In this
case, the program will iteratively reweight the data based
on a robust scale estimate, in order to converge to a
solution insensitive to outliers. This may be handy when
separating a "regional" field from a
"residual" which should have non-zero mean, such
as a local mountain on a regional surface.</p>
<p style="margin-left:11%; margin-top: 1em">If data file
has values set to NaN, these will be ignored during fitting;
if output files are written, these will also have NaN in the
same locations.</p>
<p style="margin-left:11%; margin-top: 1em">No space
between the option flag and the associated arguments.
<i><br>
grdfile</i></p>
<p style="margin-left:22%;">The name of a 2-D binary grid
file.</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 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">[<b>r</b>]<i>n_model</i>
sets the number of model parameters to fit. Append <b>r</b>
for robust fit.</p></td>
</table>
<a name="OPTIONS"></a>
<h2>OPTIONS</h2>
<p style="margin-left:11%; margin-top: 1em">No space
between the option flag and the associated arguments.</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 style="margin-top: 1em" valign="top"><b>−D</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Write the
difference (input data - trend) to the file
<i>diff.grd</i>.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−T</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Write the fitted
trend to the file <i>trend.grd</i>.</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>−W</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">If
<i>weight.grd</i> exists, it will be read and used to solve
a weighted least-squares problem. [Default: Ordinary
least-squares fit.] If the robust option has been selected,
the weights used in the robust fit will be written to
<i>weight.grd</i>.</p> </td>
</table>
<a name="REMARKS"></a>
<h2>REMARKS</h2>
<p style="margin-left:11%; margin-top: 1em">The domain of x
and y will be shifted and scaled to [-1, 1] and the basis
functions are built from Legendre polynomials. These have a
numerical advantage in the form of the matrix which must be
inverted and allow more accurate solutions. NOTE: The model
parameters listed with <b>−V</b> are Legendre
polynomial coefficients; they are not numerically equivalent
to the m#s in the equation described above. The description
above is to allow the user to match <b>−N</b> with the
order of the polynomial surface. See <b><A HREF="grdmath.html">grdmath</A></b> if you
need to evaluate the trend using the reported
coefficients.</p>
<a name="GRID FILE FORMATS"></a>
<h2>GRID FILE FORMATS</h2>
<p style="margin-left:11%; margin-top: 1em">By default
<b><A HREF="GMT.html">GMT</A></b> writes out grid as single precision floats in a
COARDS-complaint netCDF file format. However, <b><A HREF="GMT.html">GMT</A></b> is
able to produce grid files in many other commonly used grid
file formats and also facilitates so called
"packing" of grids, writing out floating point
data as 2- or 4-byte integers. To specify the precision,
scale and offset, the user should add the suffix
<b>=</b><i>id</i>[<b>/</b><i>scale</i><b>/</b><i>offset</i>[<b>/</b><i>nan</i>]],
where <i>id</i> is a two-letter identifier of the grid type
and precision, and <i>scale</i> and <i>offset</i> are
optional scale factor and offset to be applied to all grid
values, and <i>nan</i> is the value used to indicate missing
data. When reading grids, the format is generally
automatically recognized. If not, the same suffix can be
added to input grid file names. See <b><A HREF="grdreformat.html">grdreformat</A></b>(1)
and Section 4.17 of the GMT Technical Reference and Cookbook
for more information.</p>
<p style="margin-left:11%; margin-top: 1em">When reading a
netCDF file that contains multiple grids, <b><A HREF="GMT.html">GMT</A></b> will
read, by default, the first 2-dimensional grid that can find
in that file. To coax <b><A HREF="GMT.html">GMT</A></b> into reading another
multi-dimensional variable in the grid file, append
<b>?</b><i>varname</i> to the file name, where
<i>varname</i> is the name of the variable. Note that you
may need to escape the special meaning of <b>?</b> in your
shell program by putting a backslash in front of it, or by
placing the filename and suffix between quotes or double
quotes. The <b>?</b><i>varname</i> suffix can also be used
for output grids to specify a variable name different from
the default: "z". See <b><A HREF="grdreformat.html">grdreformat</A></b>(1) and
Section 4.18 of the GMT Technical Reference and Cookbook for
more information, particularly on how to read splices of 3-,
4-, or 5-dimensional grids.</p>
<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
<p style="margin-left:11%; margin-top: 1em">To remove a
planar trend from hawaii_topo.grd and write result in
hawaii_residual.grd:</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdtrend</b>
hawaii_topo.grd <b>−N</b> 3 <b>−D</b>
hawaii_residual.grd</p>
<p style="margin-left:11%; margin-top: 1em">To do a robust
fit of a bicubic surface to hawaii_topo.grd, writing the
result in hawaii_trend.grd and the weights used in
hawaii_weight.grd, and reporting the progress:</p>
<p style="margin-left:11%; margin-top: 1em"><b>grdtrend</b>
hawaii_topo.grd <b>−N</b> 10<b>r −T</b>
hawaii_trend.grd <b>−W</b> hawaii_weight.grd
<b>−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="grdfft.html">grdfft</A></i>(1), <i><A HREF="grdfilter.html">grdfilter</A></i>(1)</p>
<hr>
</body>
</html>
|