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.TH "BACKTRACKER" "1gmt" "May 21, 2019" "5.4.5" "GMT"
.SH NAME
backtracker \- Generate forward and backward flowlines and hotspot tracks
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.SH SYNOPSIS
.sp
\fBbacktracker\fP [ \fItable\fP ]  \fB\-E\fP\fIrot_file\fP|\fIlon\fP/\fIlat\fP/\fIangle\fP
[  \fB\-A\fP[\fIyoung\fP/\fIold\fP] ]
[  \fB\-D\fP\fBf\fP|\fBb\fP ]
[  \fB\-F\fP\fIdrift.txt\fP ]
[  \fB\-L\fP\fBf\fP|\fBb\fP[\fIstep\fP] ]
[  \fB\-N\fP\fIupper_age\fP ]
[  \fB\-Q\fP\fIfixed_age\fP ]
[  \fB\-S\fP\fIfilestem\fP ]
[  \fB\-T\fP\fIzero_age\fP ]
[  \fB\-V\fP[\fIlevel\fP] ]
[  \fB\-W\fP[\fBa\fP|\fBt\fP] ]
[ \fB\-b\fPbinary ]
[ \fB\-d\fPnodata ]
[ \fB\-e\fPregexp ]
[ \fB\-h\fPheaders ]
[ \fB\-i\fPflags ]
[ \fB\-o\fPflags ]
[ \fB\-:\fP[\fBi\fP|\fBo\fP] ]
.sp
\fBNote:\fP No space is allowed between the option flag and the associated arguments.
.SH DESCRIPTION
.sp
\fBbacktracker\fP reads (longitude, latitude, age) positions from
\fIinfiles\fP [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 \fB\-:\fP on how to read
(latitude,longitude,age) files.
.SH REQUIRED ARGUMENTS
.INDENT 0.0
.TP
\fB\-E\fP\fIrotfile\fP
Give file with rotation parameters. This file must contain one
record for each rotation; each record must be of the following
format:
.sp
\fIlon lat tstart [tstop] angle\fP [ \fIkhat a b c d e f g df\fP ]
.sp
where \fItstart\fP and \fItstop\fP are in Myr and \fIlon lat angle\fP are in
degrees. \fItstart\fP and \fItstop\fP are the ages of the old and young ends
of a stage. If \fItstop\fP is not present in the record then a total
reconstruction rotation is expected and \fItstop\fP is implicitly set to
0 and should not be specified for any of the records in the file. If
a covariance matrix \fBC\fP for the rotation is available it must be
specified in a format using the nine optional terms listed in
brackets. Here, \fBC\fP = (\fIg\fP/\fIkhat\fP)*[ \fIa b d; b c e; d e f\fP ]
which shows \fBC\fP made up of three row vectors. If the degrees of
freedom (\fIdf\fP) 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. You may prepend a leading + to the filename to indicate
you wish to invert the rotations.
Alternative 1: Give the filename composed of two plate IDs
separated by a hyphen (e.g., PAC\-MBL) and we will instead extract
that rotation from the GPlates rotation database. We return an error
if the rotation cannot be found.
Alternative 2: Specify \fIlon\fP/\fIlat\fP/\fIangle\fP, i.e., the longitude,
latitude, and opening angle (all in degrees and separated by /) for
a single total reconstruction rotation.
.UNINDENT
.SH OPTIONAL ARGUMENTS
.INDENT 0.0
.TP
.B \fItable\fP
One or more ASCII (or binary, see \fB\-bi\fP[\fIncols\fP][\fItype\fP]) data
table file(s) holding a number of data columns. If no tables are given
then we read from standard input.  
.UNINDENT
.INDENT 0.0
.TP
\fB\-A\fP[\fIyoung\fP/\fIold\fP]
Used in conjunction with \fB\-Lb\fP|\fBf\fP to limit the track
output to those sections whose predicted ages lie between the
specified \fIyoung\fP and \fIold\fP limits. If \fB\-LB\fP|\fBF\fP 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.
.UNINDENT
.INDENT 0.0
.TP
\fB\-Df\fP|\fBb\fP
Set the direction to go: \fB\-Df\fP will go backward in time (from
younger to older positions), while \fB\-Db\fP will go forward in time
(from older to younger positions) [Default]. Note: For \fB\-Db\fP you
are specifying the age at the given location, whereas for \fB\-Df\fP
you are not; instead you specify the age at the reconstructed point.
.UNINDENT
.INDENT 0.0
.TP
\fB\-F\fP\fIdrift.txt\fP
Supply a file with lon, lat, age records that describe the history
of hotspot motion for the current hotspot. 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].
.UNINDENT
.INDENT 0.0
.TP
\fB\-Lf\fP|\fBb\fP[\fIstep\fP]
Specify a sampled path between initial and final position: \fB\-Lf\fP
will draw particle flowlines, while \fB\-Lb\fP will draw backtrack
(hotspot track) paths. Append sampling interval in km. If \fIstep\fP < 0 or not provided
then only the rotation times will be returned. When \fB\-LF\fP or
\fB\-LB\fP 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 \fB\-D\fP\&.
.UNINDENT
.INDENT 0.0
.TP
\fB\-N\fP\fIupper_age\fP
Set the maximum age to extend the oldest stage rotation back in time
[Default is no extension].
.UNINDENT
.INDENT 0.0
.TP
\fB\-Q\fP\fIfixed_age\fP
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.
.UNINDENT
.INDENT 0.0
.TP
\fB\-S\fP\fIfilestem\fP
When \fB\-L\fP is set, the tracks are normally written to \fIstdout\fP as a
multisegment file. Specify a \fIfilestem\fP to have each track written
to \fIfilestem.#\fP, where \fI#\fP is the track number. The track number is
also copied to the 4th output column.
.UNINDENT
.INDENT 0.0
.TP
\fB\-T\fP\fIzero_age\fP
Set the current time [Default is 0 Ma].
.UNINDENT
.INDENT 0.0
.TP
\fB\-V\fP[\fIlevel\fP] (more ...)
Select verbosity level [c].  
.UNINDENT
.INDENT 0.0
.TP
\fB\-W\fP[\fBa\fP|\fBt\fP]
Rotates the given input (lon,lat,t) and calculates the confidence
ellipse for the projected point. The input point \fImust\fP have a time
coordinate that exactly matches a particular total reconstruction
rotation time, otherwise the point will be skipped. Append \fBt\fP or
\fBa\fP 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 \fB\-D\fP for the direction of
rotation.
.UNINDENT
.INDENT 0.0
.TP
\fB\-bi\fP[\fIncols\fP][\fBt\fP] (more ...)
Select native binary input. [Default is 3 input columns].
.UNINDENT
.INDENT 0.0
.TP
\fB\-bo\fP[\fIncols\fP][\fItype\fP] (more ...)
Select native binary output. [Default is same as input].
.UNINDENT
.INDENT 0.0
.TP
\fB\-d\fP[\fBi\fP|\fBo\fP]\fInodata\fP (more ...)
Replace input columns that equal \fInodata\fP with NaN and do the reverse on output.  
.UNINDENT
.INDENT 0.0
.TP
\fB\-e\fP[\fB~\fP]\fI"pattern"\fP \fB|\fP \fB\-e\fP[\fB~\fP]/\fIregexp\fP/[\fBi\fP] (more ...)
Only accept data records that match the given pattern.  
.UNINDENT
.INDENT 0.0
.TP
\fB\-h\fP[\fBi\fP|\fBo\fP][\fIn\fP][\fB+c\fP][\fB+d\fP][\fB+r\fP\fIremark\fP][\fB+r\fP\fItitle\fP] (more ...)
Skip or produce header record(s).  
.UNINDENT
.INDENT 0.0
.TP
\fB\-i\fP\fIcols\fP[\fB+l\fP][\fB+s\fP\fIscale\fP][\fB+o\fP\fIoffset\fP][,\fI\&...\fP] (more ...)
Select input columns and transformations (0 is first column).
.UNINDENT
.INDENT 0.0
.TP
\fB\-o\fP\fIcols\fP[,...] (more ...)
Select output columns (0 is first column).
.UNINDENT
.INDENT 0.0
.TP
\fB\-:\fP[\fBi\fP|\fBo\fP] (more ...)
Swap 1st and 2nd column on input and/or output.
.UNINDENT
.INDENT 0.0
.TP
\fB\-^\fP or just \fB\-\fP
Print a short message about the syntax of the command, then exits (NOTE: on Windows just use \fB\-\fP).
.TP
\fB\-+\fP or just \fB+\fP
Print an extensive usage (help) message, including the explanation of
any module\-specific option (but not the GMT common options), then exits.
.TP
\fB\-?\fP or no arguments
Print a complete usage (help) message, including the explanation of all options, then exits.
.UNINDENT
.SH GEODETIC VERSUS GEOCENTRIC COORDIINATES
.sp
All spherical rotations are applied to geocentric coordinates.
This means that incoming data points and grids are considered
to represent geodetic coordinates and must first
be converted to geocentric coordinates. Rotations are then applied, and the
final reconstructed points are converted back to geodetic
coordinates.  This default behavior can be bypassed if the
ellipsoid setting PROJ_ELLIPSOID
is changed to Sphere.
.SH EXAMPLES
.sp
To backtrack the (x,y,t) points in the file seamounts.txt to their origin
(presumably the hotspot), using the DC85.txt Euler poles, run
.INDENT 0.0
.INDENT 3.5
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
gmt backtracker seamounts.txt \-Db \-EDC85.txt > newpos.txt
.ft P
.fi
.UNINDENT
.UNINDENT
.UNINDENT
.UNINDENT
.sp
To project flowlines forward from the (x,y,t) points stored in several
3\-column, binary, double precision files, run
.INDENT 0.0
.INDENT 3.5
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
gmt backtracker points.\e* \-Df \-EDC85.txt \-Lf25 \-bo \-bi3 > lines.b
.ft P
.fi
.UNINDENT
.UNINDENT
.UNINDENT
.UNINDENT
.sp
This file can then be plotted with psxy\&.
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.txt), try
.INDENT 0.0
.INDENT 3.5
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
echo 204 19 80 | gmt backtracker \-Df \-EPAC_APM.txt \-Lb1 > path.txt
.ft P
.fi
.UNINDENT
.UNINDENT
.UNINDENT
.UNINDENT
.SH NOTES
.sp
GMT distributes the EarthByte rotation model Global_EarthByte_230\-0Ma_GK07_AREPS.rot.
To use an alternate rotation file, create an environmental parameters named
\fBGPLATES_ROTATIONS\fP that points to an alternate rotation file.
.SH SEE ALSO
.sp
gmt ,
gmtpmodeler,
grdpmodeler,
grdrotater,
grdspotter,
hotspotter,
mapproject,
originator,
project,
psxy
.SH REFERENCES
.sp
Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80 (29),
p. 319.
.SH COPYRIGHT
2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
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