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<title>BACKTRACKER</title>
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<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="#COORDINATES">COORDINATES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#REFERENCES">REFERENCES</a><br>
<hr>
<h2>NAME
<a name="NAME"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">backtracker
− Reconstruct points, flowlines and hotspot tracks</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</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>−F</b><i>drift.txt</i> ] [
<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>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</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>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>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><b>−E</b></p></td>
<td width="8%"></td>
<td width="78%">
<p>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>
</table>
<p style="margin-left:22%; margin-top: 1em"><i>lon lat
tstart [tstop] angle</i> [ <i>khat a b c d e f g df</i>
]</p>
<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"
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<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em"><b>−e</b></p></td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em">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></tr>
</table>
<h2>OPTIONS
<a name="OPTIONS"></a>
</h2>
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<p style="margin-top: 1em"><b>−A</b></p></td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em">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>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−C</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>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>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p><b>−D</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>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>
<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>Supply a file with lon, lat, age records that contains
the history of hotspot motion for the current hotspot. If
given, the reconstructions will only use the 3rd data input
column (i.e., the age) to obtain the location of the hotspot
at that time, via an interpolation of the hotspot motion
history. This adjusted location is then used to reconstruct
the point or path [No drift].</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>−L</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>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>
<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>Set the maximum age to extend the oldest stage rotation
back in time [Default is no extension].</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>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>
<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>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>
<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>Set the current time [Default is 0 Ma].</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>−W</b></p></td>
<td width="7%"></td>
<td width="78%">
<p>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>
<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 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>
<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 3 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 depends on settings].</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 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>
<p style="margin-left:11%; margin-top: 1em">To compute the
predicted Hawaiian hotspot track from 0 to 80 Ma every 1 Ma,
given a history of hotspot motion file (HIdrift.txt) and a
set of total reconstruction rotations for the plate
(PAC_APM.d), try</p>
<p style="margin-left:11%; margin-top: 1em">echo 204 19 80
| <b>backtracker −Df −C −E</b> PAC_APM.d
<b>−Lb</b> 1 > path.d</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="GMT.html">GMT</A></i>(1),
<i><A HREF="project.html">project</A></i>(1), <i><A HREF="grdrotater.html">grdrotater</A></i>(1),
<i><A HREF="grdspotter.html">grdspotter</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>
<h2>REFERENCES
<a name="REFERENCES"></a>
</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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