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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>
<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>−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>
<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>−F</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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 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>
<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>
<a name="COORDINATES"></a>
<h2>COORDINATES</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>
<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="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>
<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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