backtracker − Reconstruct points, flowlines and hotspot tracks
backtracker [infile(s)] −Erotations.txt | −elon/lat/angle [ −A[young/old] ] [ −C ] [ −Df|b ] [ −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] ]
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: |
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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. |
−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. |
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−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. |
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−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. |
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−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. |
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−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. |
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−N |
Set the maximum age to extend the oldest stage rotation back in time [Default is no extension]. |
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−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. |
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−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. |
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−T |
Set the current time [Default is 0 Ma]. |
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−V |
Selects verbose mode, which will send progress reports to stderr [Default runs "silently"]. |
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−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. |
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−: |
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]. |
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−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]. |
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−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]. |
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−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. |
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 −EDC85.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 −EDC85.d −Lf25 −bo −bi3 > lines.b
This file can then be plotted with psxy −M.
GMT(1), project(1), mapproject(1), hotspotter(1), originator(1)
Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80 (29), p. 319.