1BACKTRACKER(1) Generic Mapping Tools BACKTRACKER(1)
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6 backtracker - Forward and Backward flowlines and hotspot tracks
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9 backtracker [infile(s)] -Estage_file [ -A[young/old] ] [ -C ] [ -Df|b ]
10 [ -H[i][nrec] ] [ -Lf|bstep ] [ -M[i|o][flag] ] [ -Nupper_age ] [
11 -Qfixed_age ] [ -Sfilestem ] [ -Tzero_age ] [ -V ] [ -W[a|t] ] [
12 -:[i|o] ] [ -b[i|o][s|S|d|D[ncol]|c[var1/...]] ]
13
15 backtracker reads (longitude, latitude, age) positions from infiles [or
16 standard input] and computes projected (x,y,t) coordinates using the
17 specified rotation parameters. It can either calculate final positions
18 [Default] or create a sampled track between the initial and final posi‐
19 tions. The former mode allows additional data fields after the first 3
20 columns which must have (longitude,latitude,age). See option -: on how
21 to read (latitude,longitude,age) files.
22 No space between the option flag and the associated arguments.
23 Use upper case for the option flags and lower case for modifiers.
24 infile(s)
26 Data file(s) to be projected. If not given, standard input is
27 read.
28 -E Give file with rotation poles and opening angles. This file
30 must contain one record for each rotation; each record must be
31 of the following format:
32 lon lat tstart [tstop] ccw-angle [k a b c d e f g]
34 where tstart [and tstop] are in Ma, with lon, lat, and angle in
36 degrees. For stage rotations, the oldest stage must be listed
37 first, whereas for total reconstruction rotations the youngest
38 rotation is listed first. tstart (tstop) is the age of the old
39 (young) end of the stage. A covariance matrix, if present, may
40 be given in the given format. Blank lines and records whose
41 first column contains # will be ignored.
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44 -A Used in conjunction with -Lb|f to limit the track output to
45 those sections whose predicted ages fit between the young and
46 old limits. If -LB|F is used instead then the limits apply to
47 the stage ids. If no limits are supplied then individual limits
48 for each seamount are expected in columns 4 and 5 of the input
49 file.
50 -C Expect Total Reconstruction Poles rather than Backward Stage
52 Poles [Default]. File format is similar to the stage pole for‐
53 mat except the youngest rotation must be listed first and that
54 the tstart column is optional (assumed to be 0 Ma).
55 -D Set the direction to go: -Df will go forward in time (from
57 younger to older positions), while -Db will go backward in time
58 (from older to younger positions) [Default].
59 -H Input file(s) has Header record(s). Number of header records
61 can be changed by editing your .gmtdefaults4 file. If used, GMT
62 default is 1 header record. Use -Hi if only input data should
63 have header records [Default will write out header records if
64 the input data have them]. Blank lines and lines starting with #
65 are always skipped.
66 -L Specify a sampled path between initial and final position: -Lf
68 will draw flowlines, while -Lb will draw backtrack (hotspot
69 track) paths. Append sampling interval in km. If step < 0 then
70 only the bend-times (knots) will be returned. When -LF or -LB
71 is used, the third output column will contain the stage id (1 is
72 youngest) [Default is along-track ages].
73 -M Multiple segment file(s). Segments are separated by a special
75 record. For ASCII files the first character must be flag
76 [Default is '>']. For binary files all fields must be NaN and
77 -b must set the number of output columns explicitly. By default
78 the -M setting applies to both input and output. Use -Mi and
79 -Mo to give separate settings.
80 -N Set the maximum age to extend the oldest stage back in time
82 [Default is no extension].
83 -Q Assign a fixed age to all positions. Only lon, lat input is
85 expected.
86 -S When -L is set, the tracks are normally written to stdout as a
88 multisegment file. Specify a filestem to have each track writ‐
89 ten to filestem.#, where # is the track number. The track num‐
90 ber is also copied to the 4th output column.
91 -T Set the current time [Default is 0 Ma].
93 -V Selects verbose mode, which will send progress reports to stderr
95 [Default runs "silently"].
96 -W Rotates the given input (lon,lat,t) and calculates the confi‐
98 dence ellipse for the projected point. The input point must
99 have a time coordinate that matches a particular finite rotation
100 time, otherwise the point will be skipped. Append t or a to
101 output time or angle, respectively, after the projected lon,
102 lat. After these 2-3 items, we write azimuth, major, minor (in
103 km) for the 95% confidence ellipse.
104 -: Toggles between (longitude,latitude) and (latitude,longitude)
106 input and/or output. [Default is (longitude,latitude)]. Append
107 i to select input only or o to select output only. [Default
108 affects both].
109 -bi Selects binary input. Append s for single precision [Default is
111 d (double)]. Uppercase S or D will force byte-swapping.
112 Optionally, append ncol, the number of columns in your binary
113 input file if it exceeds the columns needed by the program. Or
114 append c if the input file is netCDF. Optionally, append
115 var1/var2/... to specify the variables to be read. [Default is
116 3 input columns].
117 -bo Selects binary output. Append s for single precision [Default
119 is d (double)]. Uppercase S or D will force byte-swapping.
120 Optionally, append ncol, the number of desired columns in your
121 binary output file. [Default depends on settings].
122
124 To backtrack the (x,y,t) points in the file seamounts.d to their origin
125 (presumably the hotspot), using the DC85.d Euler poles, run
126 backtracker seamounts.d -Db -EDC85.d > newpos.d
128 To project flowlines forward from the (x,y,t) points stored in several
130 3-column, binary, double precision files, run
131 backtracker points.* -Df -EDC85.d -Lf25 -bo -bi3 > lines.b
133 This file can then be plotted with psxy -M.
135
137 GMT(1), project(1), mapproject(1), hotspotter(1), originator(1)
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140 Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80
141 (29), p. 319.
142GMT 4.3.1 15 May 2008 BACKTRACKER(1)