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<title>FILTER1D</title>
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<h1 align="center">FILTER1D</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="#ASCII FORMAT PRECISION">ASCII FORMAT PRECISION</a><br>
<a href="#EXAMPLES">EXAMPLES</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">filter1d
− Time domain filtering of 1-D time series</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>filter1d</b>
[ <i>infile</i> ]
<b>−F</b><i><type><width></i>[<i>mode</i>]
[ <b>−D</b><i>increment</i> ] [ <b>−E</b> ] [
<b>−H</b>[<b>i</b>][<i>nrec</i>] ] [
<b>−I</b><i>ignore_val</i> ] [
<b>−L</b><i>lack_width</i> ] [
<b>−N</b><i>n_cols/t_col</i> ] [
<b>−Q</b><i>q_factor</i> ] [
<b>−S</b><i>symmetry_factor</i> ] [
<b>−T</b><i>start/stop/int</i> ] [ <b>−V</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>−f</b>[<b>i</b>|<b>o</b>]<i>colinfo</i> ]</p>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>filter1d</b>
is a general time domain filter for multiple column time
series data. The user specifies the number of columns of
input and which column is the time. (See <b>−N</b>
option below). The fastest operation occurs when the input
time series are equally spaced and have no gaps or outliers
and the special options are not needed. <b>filter1d</b> has
options <b>-L</b>, <b>-Q</b>, and <b>-S</b> for unevenly
sampled data with gaps.</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><i>infile</i></p></td>
<td width="2%"></td>
<td width="78%">
<p>Multi-column ASCII (or binary, see <b>−b</b>) file
holding data values to be filtered.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p><b>−F</b></p></td>
<td width="2%"></td>
<td width="78%">
<p>Sets the filter type. Choose among convolution and
non-convolution filters. Append the filter code followed by
the full filter <i>width</i> in same units as time column.
Available convolution filters are:</p></td></tr>
</table>
<p style="margin-left:22%;">(<b>b</b>) Boxcar: All weights
are equal. <br>
(<b>c</b>) Cosine Arch: Weights follow a cosine arch curve.
<br>
(<b>g</b>) Gaussian: Weights are given by the Gaussian
function. <br>
(<b>f</b>) Custom: Instead of <i>width</i> give name of a
one-column file with your own weight coefficients. <br>
Non-convolution filters are: <br>
(<b>m</b>) Median: Returns median value. <br>
(<b>p</b>) Maximum likelihood probability (a mode
estimator): Return modal value. If more than one mode is
found we return their average value. Append - or + to the
filter width if you rather want to return the smallest or
largest of the modal values. <br>
(<b>l</b>) Lower: Return the minimum of all values. <br>
(<b>L</b>) Lower: Return minimum of all positive values
only. <br>
(<b>u</b>) Upper: Return maximum of all values. <br>
(<b>U</b>) Upper: Return maximum or all negative values
only. <br>
Upper case type <b>B, C, G, M, P, F</b> will use robust
filter versions: i.e., replace outliers (2.5 L1 scale off
median) with median during filtering. <br>
In the case of <b>L|U</b> it is possible that no data passes
the initial sign test; in that case the filter will return
0.0.</p>
<h2>OPTIONS
<a name="OPTIONS"></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="4%">
<p style="margin-top: 1em"><b>−D</b></p></td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em"><i>increment</i> is used when
series is NOT equidistantly sampled. Then <i>increment</i>
will be the abscissae resolution, i.e., all abscissae will
be rounded off to a multiple of <i>increment</i>.
Alternatively, resample data with <b><A HREF="sample1d.html">sample1d</A></b>.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−E</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Include Ends of time series in output. Default loses
half the filter-width of data at each end.</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>−I</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>To ignore values; If an input value equals
<i>ignore_val</i> it will be set to NaN.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−L</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Checks for Lack of data condition. If input data has a
gap exceeding <i>width</i> then no output will be given at
that point [Default does not check Lack].</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>Sets number of columns in input and which column
contains the independent variable (time). The left-most
column is # 0, the right-most is # (<i>n_cols</i> - 1).
[Default is <i>n_cols</i> = 2, <i>t_col</i> = 0; i.e., file
has t, f(t) pairs].</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>assess Quality of output value by checking mean weight
in convolution. Enter <i>q_factor</i> between 0 and 1. If
mean weight < <i>q_factor</i>, output is suppressed at
this point [Default does not check Quality].</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>Checks symmetry of data about window center. Enter a
factor between 0 and 1. If ( (abs(n_left - n_right)) /
(n_left + n_right) ) > <i>factor</i>, then no output will
be given at this point [Default does not check
Symmetry].</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−T</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>Make evenly spaced timesteps from <i>start</i> to
<i>stop</i> by <i>int</i> [Default uses input times].</p></td></tr>
<tr valign="top" align="left">
<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>−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.</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>−f</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>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></tr>
</table>
<h2>ASCII FORMAT PRECISION
<a name="ASCII FORMAT PRECISION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">The ASCII
output formats of numerical data are controlled by
parameters in your .gmtdefaults4 file. Longitude and
latitude are formatted according to
<b><A HREF="gmtdefaults.html#OUTPUT_DEGREE_FORMAT">OUTPUT_DEGREE_FORMAT</A></b>, whereas other values are
formatted according to <b><A HREF="gmtdefaults.html#D_FORMAT">D_FORMAT</A></b>. Be aware that the
format in effect can lead to loss of precision in the
output, which can lead to various problems downstream. If
you find the output is not written with enough precision,
consider switching to binary output (<b>−bo</b> if
available) or specify more decimals using the
<b><A HREF="gmtdefaults.html#D_FORMAT">D_FORMAT</A></b> setting.</p>
<h2>EXAMPLES
<a name="EXAMPLES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">To filter the
data set in the file cruise.gmtd containing evenly spaced
gravity, magnetics, topography, and distance (in m) with a
10 km Gaussian filter, removing outliers, and output a
filtered value every 2 km between 0 and 100 km:</p>
<p style="margin-left:11%; margin-top: 1em"><b>filter1d</b>
cruise.gmtd <b>−T</b> 0/1.0e5/2000 <b>−FG</b>
10000 <b>−N</b> 4/3 <b>−V</b> >
filtered_cruise.gmtd</p>
<p style="margin-left:11%; margin-top: 1em">Data along
track often have uneven sampling and gaps which we do not
want to interpolate using <b><A HREF="sample1d.html">sample1d</A></b>. To find the
median depth in a 50 km window every 25 km along the track
of cruise v3312, stored in v3312.dt, checking for gaps of
10km and asymmetry of 0.3:</p>
<p style="margin-left:11%; margin-top: 1em"><b>filter1d</b>
v3312.dt <b>−FM</b> 50 <b>−T</b> 0/100000/25
<b>−L</b> 10 <b>−S</b> 0.3 >
v3312_filt.dt</p>
<h2>SEE ALSO
<a name="SEE ALSO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><i><A HREF="GMT.html">GMT</A></i>(1),
<i><A HREF="sample1d.html">sample1d</A></i>(1)</p>
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