DragonFly On-Line Manual Pages
BACKTRACKER(1) Generic Mapping Tools BACKTRACKER(1)
NAME
backtracker - Reconstruct points, flowlines and hotspot tracks
SYNOPSIS
backtracker [infile(s)] -Erotations.txt | -elon/lat/angle [
-A[young/old] ] [ -C ] [ -Df|b ] [ -Fdrift.txt ] [ -H[i][nrec] ] [
-Lf|bstep ] [ -Nupper_age ] [ -Qfixed_age ] [ -Sfilestem ] [ -Tzero_age
] [ -V ] [ -W[a|t] ] [ -:[i|o] ] [ -b[i|o][s|S|d|D[ncol]|c[var1/...]] ]
[ -m[i|o][flag] ]
DESCRIPTION
backtracker reads (longitude, latitude, age) positions from infiles [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 -: on how to read
(latitude,longitude,age) files.
No space between the option flag and the associated arguments.
Use upper case for the option flags and lower case for modifiers.
infile(s)
Data file(s) to be projected. If not given, standard input is
read.
-E Give file with rotation parameters. This file must contain one
record for each rotation; each record must be of the following
format:
lon lat tstart [tstop] angle [ khat a b c d e f g df ]
where tstart and tstop are in Myr and lon lat angle are in
degrees. tstart and tstop are the ages of the old and young
ends of a stage. If -C is set then a total reconstruction
rotation is expected and tstop is implicitly set to 0 and should
not be specified in the file. If a covariance matrix C for the
rotation is available it must be specified in a format using the
nine optional terms listed in brackets. Here, C = (g/khat)*[ a
b d; b c e; d e f ] which shows C made up of three row vectors.
If the degrees of freedom (df) 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.
-e 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.
OPTIONS
-A Used in conjunction with -Lb|f to limit the track output to
those sections whose predicted ages lie between the specified
young and old limits. If -LB|F 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.
-C Expect Total Reconstruction Rotations rather than Forward Stage
Rotations [Default]. File format is similar to the stage pole
format except that the tstart column is not present (assumed to
be 0 Ma). Requires -E.
-D Set the direction to go: -Df will go backward in time (from
younger to older positions), while -Db will go forward in time
(from older to younger positions) [Default]. Note: For -Db you
are specifying the age at the given location, whereas for -Df
you are not; instead you specify the age at the reconstructed
point.
-F 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].
-H Input file(s) has header record(s). If used, the default number
of header records is N_HEADER_RECS. Use -Hi 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.
-L Specify a sampled path between initial and final position: -Lf
will draw particle flowlines, while -Lb will draw backtrack
(hotspot track) paths. Append sampling interval in km. If step
< 0 then only the rotation times will be returned. When -LF or
-LB 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 -D.
-N Set the maximum age to extend the oldest stage rotation back in
time [Default is no extension].
-Q 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.
-S When -L is set, the tracks are normally written to stdout as a
multisegment file. Specify a filestem to have each track
written to filestem.#, where # is the track number. The track
number is also copied to the 4th output column.
-T Set the current time [Default is 0 Ma].
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
-W Rotates the given input (lon,lat,t) and calculates the
confidence ellipse for the projected point. The input point
must have a time coordinate that exactly matches a particular
finite rotation time, otherwise the point will be skipped.
Append t or a 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 -D for
the direction of rotation.
-: Toggles between (longitude,latitude) and (latitude,longitude)
input and/or output. [Default is (longitude,latitude)]. Append
i to select input only or o to select output only. [Default
affects both].
-bi Selects binary input. Append s for single precision [Default is
d (double)]. Uppercase S or D will force byte-swapping.
Optionally, append ncol, the number of columns in your binary
input file if it exceeds the columns needed by the program. Or
append c if the input file is netCDF. Optionally, append
var1/var2/... to specify the variables to be read. [Default is
3 input columns].
-bo Selects binary output. Append s for single precision [Default
is d (double)]. Uppercase S or D will force byte-swapping.
Optionally, append ncol, the number of desired columns in your
binary output file. [Default depends on settings].
-m Multiple segment file(s). Segments are separated by a special
record. For ASCII files the first character must be flag
[Default is '>']. For binary files all fields must be NaN and
-b must set the number of output columns explicitly. By default
the -m setting applies to both input and output. Use -mi and
-mo to give separate settings to input and output.
EXAMPLES
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
backtracker seamounts.d -Db -E DC85.d > newpos.d
To project flowlines forward from the (x,y,t) points stored in several
3-column, binary, double precision files, run
backtracker points.* -Df -E DC85.d -Lf 25 -bo -bi3 > lines.b
This file can then be plotted with psxy -M.
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
echo 204 19 80 | backtracker -Df -C -E PAC_APM.d -Lb 1 > path.d
COORDINATES
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.
SEE ALSO
GMT(1), project(1), grdrotater(1), grdspotter(1), mapproject(1),
hotspotter(1), originator(1)
REFERENCES
Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80
(29), p. 319.
GMT 4.5.14 1 Nov 2015 BACKTRACKER(1)