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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>
<a name="NAME"></a>
<h2>NAME</h2>
<p style="margin-left:11%; margin-top: 1em">filter1d
− Time domain filtering of 1-D time series</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</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>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</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 style="margin-top: 1em" valign="top"><i>infile</i></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Multi-column ASCII
(or binary, see <b>−b</b>) file holding data values to
be filtered.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>−F</b></p> </td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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>
</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>
<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="4%">
<p style="margin-top: 1em" valign="top"><b>−D</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top"><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 valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−E</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Include Ends of
time series in output. Default loses half the filter-width
of data at each end.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−H</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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 valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−I</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">To ignore values;
If an input value equals <i>ignore_val</i> it will be set to
NaN.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−L</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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 valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−N</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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 valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Q</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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 valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−S</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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 valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−T</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Make evenly spaced
timesteps from <i>start</i> to <i>stop</i> by <i>int</i>
[Default uses input times].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−V</b></p> </td>
<td width="7%"></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="4%">
<p style="margin-top: 1em" valign="top"><b>−bi</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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 valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−bo</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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 valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−f</b></p> </td>
<td width="7%"></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="ASCII FORMAT PRECISION"></a>
<h2>ASCII FORMAT PRECISION</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>
<a name="EXAMPLES"></a>
<h2>EXAMPLES</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>
<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="sample1d.html">sample1d</A></i>(1)</p>
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