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<title>BACKTRACKER</title>
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<body bgcolor="#ffffff">
<h1 align=center>BACKTRACKER</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="#SEE ALSO">SEE ALSO</a><br>
<a href="#REFERENCES">REFERENCES</a><br>
<hr>
<a name="NAME"></a>
<h2>NAME</h2>
<p style="margin-left:11%; margin-top: 1em">backtracker
− Reconstruct points, flowlines and hotspot tracks</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<p style="margin-left:11%; margin-top: 1em"><b>backtracker</b>
[<i>infile(s)</i>] <b>−E</b><i>rotations.txt</i> |
<b>−e</b><i>lon</i>/<i>lat</i>/<i>angle</i> [
<b>−A</b>[<i>young</i>/<i>old</i>] ] [ <b>−C</b>
] [ <b>−Df</b>|<b>b</b> ] [
<b>−H</b>[<b>i</b>][<i>nrec</i>] ] [
<b>−Lf</b>|<b>b</b><i>step</i> ] [
<b>−N</b><i>upper_age</i> ] [
<b>−Q</b><i>fixed_age</i> ] [
<b>−S</b><i>filestem</i> ] [
<b>−T</b><i>zero_age</i> ] [ <b>−V</b> ] [
<b>−W</b>[<b>a</b>|<b>t</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>[<b>i</b>|<b>o</b>][<i>flag</i>] ]</p>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>backtracker</b>
reads (longitude, latitude, age) positions from
<i>infiles</i> [or standard input] and computes rotated
(x,y,t) coordinates using the specified rotation parameters.
It can either calculate final positions [Default] or create
a sampled track (flowline or hotspot track) between the
initial and final positions. The former mode allows
additional data fields after the first 3 columns which must
have (longitude,latitude,age). See option <b>−:</b> on
how to read (latitude,longitude,age) files.</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="8%"></td>
<td width="7%"></td>
<td width="85%">
<p valign="top">No space between the option flag and the
associated arguments. Use upper case for the option flags
and lower case for modifiers.</p></td>
</table>
<p style="margin-left:11%;"><i>infile(s)</i></p>
<p style="margin-left:22%;">Data file(s) to be projected.
If not given, standard input is read.</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>−E</b></p> </td>
<td width="4%"></td>
<td width="82%">
<p style="margin-top: 1em" valign="top">Give file with
rotation parameters. This file must contain one record for
each rotation; each record must be of the following
format:</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%"></td>
<td width="4%"></td>
<td width="82%">
<p valign="top"><i>lon lat tstart [tstop] angle</i> [
<i>khat a b c d e f g df</i> ]</p></td>
</table>
<p style="margin-left:22%; margin-top: 1em">where
<i>tstart</i> and <i>tstop</i> are in Myr and <i>lon lat
angle</i> are in degrees. <i>tstart</i> and <i>tstop</i> are
the ages of the old and young ends of a stage. If
<b>−C</b> is set then a total reconstruction rotation
is expected and <i>tstop</i> is implicitly set to 0 and
should not be specified in the file. If a covariance matrix
<b>C</b> for the rotation is available it must be specified
in a format using the nine optional terms listed in
brackets. Here, <b>C</b> = (<i>g</i>/<i>khat</i>)*[ <i>a b
d; b c e; d e f</i> ] which shows <b>C</b> made up of three
row vectors. If the degrees of freedom (<i>df</i>) in
fitting the rotation is 0 or not given it is set to 10000.
Blank lines and records whose first column contains # will
be ignored.</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>−e</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Alternatively,
specify the longitude, latitude, and opening angle (all in
degrees and separated by /) for a single total
reconstruction rotation that should be applied to all input
points.</p> </td>
</table>
<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>−A</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Used in conjunction
with <b>−Lb</b>|<b>f</b> to limit the track output to
those sections whose predicted ages lie between the
specified <i>young</i> and <i>old</i> limits. If
<b>−LB</b>|<b>F</b> is used instead then the limits
apply to the stage ids (id 1 is the youngest stage). If no
limits are specified then individual limits for each record
are expected in columns 4 and 5 of the input file.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−C</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Expect Total
Reconstruction Rotations rather than Forward Stage Rotations
[Default]. File format is similar to the stage pole format
except that the <i>tstart</i> column is not present (assumed
to be 0 Ma). Requires <b>−E</b>.</p></td>
<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">Set the direction
to go: <b>−Df</b> will go backward in time (from
younger to older positions), while <b>−Db</b> will go
forward in time (from older to younger positions) [Default].
Note: For <b>−Db</b> you are specifying the age at the
given location, whereas for <b>−Df</b> you are not;
instead you specify the age at the reconstructed point.</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>−L</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Specify a sampled
path between initial and final position: <b>−Lf</b>
will draw particle flowlines, while <b>−Lb</b> will
draw backtrack (hotspot track) paths. Append sampling
interval in km. If <i>step</i> < 0 then only the rotation
times will be returned. When <b>−LF</b> or
<b>−LB</b> is used, the third output column will
contain the stage id (1 is youngest) [Default is along-track
predicted ages]. You can control the direction of the paths
by using <b>−D</b>.</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">Set the maximum age
to extend the oldest stage rotation back in time [Default is
no extension].</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">Assign a fixed age
to all positions. Only lon, lat input is expected [Default
expects longitude, latitude, age]. Useful when the input are
points defining isochrons.</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">When
<b>−L</b> is set, the tracks are normally written to
stdout as a multisegment file. Specify a <i>filestem</i> to
have each track written to <i>filestem.#</i>, where <i>#</i>
is the track number. The track number is also copied to the
4th output column.</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">Set the current
time [Default is 0 Ma].</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>−W</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Rotates the given
input (lon,lat,t) and calculates the confidence ellipse for
the projected point. The input point <i>must</i> have a time
coordinate that exactly matches a particular finite rotation
time, otherwise the point will be skipped. Append <b>t</b>
or <b>a</b> to output time or angle, respectively, after the
projected lon, lat. After these 2-3 items, we write azimuth,
major, minor (in km) for the 95% confidence ellipse. See
<b>−D</b> for the direction of rotation.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−:</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Toggles between
(longitude,latitude) and (latitude,longitude) input and/or
output. [Default is (longitude,latitude)]. Append <b>i</b>
to select input only or <b>o</b> to select output only.
[Default affects both].</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. [Default is 3 input columns].</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 depends on settings].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−m</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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>
</table>
<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
<p style="margin-left:11%; margin-top: 1em">To backtrack
the (x,y,t) points in the file seamounts.d to their origin
(presumably the hotspot), using the DC85.d Euler poles,
run</p>
<p style="margin-left:11%; margin-top: 1em"><b>backtracker</b>
seamounts.d <b>−Db −E</b>DC85.d >
newpos.d</p>
<p style="margin-left:11%; margin-top: 1em">To project
flowlines forward from the (x,y,t) points stored in several
3-column, binary, double precision files, run</p>
<p style="margin-left:11%; margin-top: 1em"><b>backtracker</b>
points.* <b>−Df −E</b>DC85.d <b>−Lf</b>25
<b>−bo −bi</b><i>3</i> > lines.b</p>
<p style="margin-left:11%; margin-top: 1em">This file can
then be plotted with <b>psxy −M</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="project.html">project</A></i>(1), <i><A HREF="mapproject.html">mapproject</A></i>(1),
<i><A HREF="hotspotter.html">hotspotter</A></i>(1), <i><A HREF="originator.html">originator</A></i>(1)</p>
<a name="REFERENCES"></a>
<h2>REFERENCES</h2>
<p style="margin-left:11%; margin-top: 1em">Wessel, P.,
1999, "Hotspotting" tools released, EOS Trans.
AGU, 80 (29), p. 319.</p>
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