1BACKTRACKER(1) Generic Mapping Tools BACKTRACKER(1)
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6 backtracker - Reconstruct points, flowlines and hotspot tracks
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9 backtracker [infile(s)] -Erotations.txt | -elon/lat/angle [
10 -A[young/old] ] [ -C ] [ -Df|b ] [ -Fdrift.txt ] [ -H[i][nrec] ] [
11 -Lf|bstep ] [ -Nupper_age ] [ -Qfixed_age ] [ -Sfilestem ] [ -Tzero_age
12 ] [ -V ] [ -W[a|t] ] [ -:[i|o] ] [ -b[i|o][s|S|d|D[ncol]|c[var1/...]] ]
13 [ -m[i|o][flag] ]
14
16 backtracker reads (longitude, latitude, age) positions from infiles [or
17 standard input] and computes rotated (x,y,t) coordinates using the
18 specified rotation parameters. It can either calculate final positions
19 [Default] or create a sampled track (flowline or hotspot track) between
20 the initial and final positions. The former mode allows additional
21 data fields after the first 3 columns which must have (longitude,lati‐
22 tude,age). See option -: on how to read (latitude,longitude,age)
23 files.
24 No space between the option flag and the associated arguments.
25 Use upper case for the option flags and lower case for modifiers.
26 infile(s)
28 Data file(s) to be projected. If not given, standard input is
29 read.
30 -E Give file with rotation parameters. This file must contain one
32 record for each rotation; each record must be of the following
33 format:
34 lon lat tstart [tstop] angle [ khat a b c d e f g df ]
36 where tstart and tstop are in Myr and lon lat angle are in
38 degrees. tstart and tstop are the ages of the old and young
39 ends of a stage. If -C is set then a total reconstruction rota‐
40 tion is expected and tstop is implicitly set to 0 and should not
41 be specified in the file. If a covariance matrix C for the
42 rotation is available it must be specified in a format using the
43 nine optional terms listed in brackets. Here, C = (g/khat)*[ a
44 b d; b c e; d e f ] which shows C made up of three row vectors.
45 If the degrees of freedom (df) in fitting the rotation is 0 or
46 not given it is set to 10000. Blank lines and records whose
47 first column contains # will be ignored.
48 -e Alternatively, specify the longitude, latitude, and opening
50 angle (all in degrees and separated by /) for a single total
51 reconstruction rotation that should be applied to all input
52 points.
53
55 -A Used in conjunction with -Lb|f to limit the track output to
56 those sections whose predicted ages lie between the specified
57 young and old limits. If -LB|F is used instead then the limits
58 apply to the stage ids (id 1 is the youngest stage). If no lim‐
59 its are specified then individual limits for each record are
60 expected in columns 4 and 5 of the input file.
61 -C Expect Total Reconstruction Rotations rather than Forward Stage
63 Rotations [Default]. File format is similar to the stage pole
64 format except that the tstart column is not present (assumed to
65 be 0 Ma). Requires -E.
66 -D Set the direction to go: -Df will go backward in time (from
68 younger to older positions), while -Db will go forward in time
69 (from older to younger positions) [Default]. Note: For -Db you
70 are specifying the age at the given location, whereas for -Df
71 you are not; instead you specify the age at the reconstructed
72 point.
73 -F Supply a file with lon, lat, age records that contains the his‐
75 tory of hotspot motion for the current hotspot. If given, the
76 reconstructions will only use the 3rd data input column (i.e.,
77 the age) to obtain the location of the hotspot at that time, via
78 an interpolation of the hotspot motion history. This adjusted
79 location is then used to reconstruct the point or path [No
80 drift].
81 -H Input file(s) has header record(s). If used, the default number
83 of header records is N_HEADER_RECS. Use -Hi if only input data
84 should have header records [Default will write out header
85 records if the input data have them]. Blank lines and lines
86 starting with # are always skipped.
87 -L Specify a sampled path between initial and final position: -Lf
89 will draw particle flowlines, while -Lb will draw backtrack
90 (hotspot track) paths. Append sampling interval in km. If step
91 < 0 then only the rotation times will be returned. When -LF or
92 -LB is used, the third output column will contain the stage id
93 (1 is youngest) [Default is along-track predicted ages]. You
94 can control the direction of the paths by using -D.
95 -N Set the maximum age to extend the oldest stage rotation back in
97 time [Default is no extension].
98 -Q Assign a fixed age to all positions. Only lon, lat input is
100 expected [Default expects longitude, latitude, age]. Useful
101 when the input are points defining isochrons.
102 -S When -L is set, the tracks are normally written to stdout as a
104 multisegment file. Specify a filestem to have each track writ‐
105 ten to filestem.#, where # is the track number. The track num‐
106 ber is also copied to the 4th output column.
107 -T Set the current time [Default is 0 Ma].
109 -V Selects verbose mode, which will send progress reports to stderr
111 [Default runs "silently"].
112 -W Rotates the given input (lon,lat,t) and calculates the confi‐
114 dence ellipse for the projected point. The input point must
115 have a time coordinate that exactly matches a particular finite
116 rotation time, otherwise the point will be skipped. Append t or
117 a to output time or angle, respectively, after the projected
118 lon, lat. After these 2-3 items, we write azimuth, major, minor
119 (in km) for the 95% confidence ellipse. See -D for the direc‐
120 tion of rotation.
121 -: Toggles between (longitude,latitude) and (latitude,longitude)
123 input and/or output. [Default is (longitude,latitude)]. Append
124 i to select input only or o to select output only. [Default
125 affects both].
126 -bi Selects binary input. Append s for single precision [Default is
128 d (double)]. Uppercase S or D will force byte-swapping.
129 Optionally, append ncol, the number of columns in your binary
130 input file if it exceeds the columns needed by the program. Or
131 append c if the input file is netCDF. Optionally, append
132 var1/var2/... to specify the variables to be read. [Default is
133 3 input columns].
134 -bo Selects binary output. Append s for single precision [Default
136 is d (double)]. Uppercase S or D will force byte-swapping.
137 Optionally, append ncol, the number of desired columns in your
138 binary output file. [Default depends on settings].
139 -m Multiple segment file(s). Segments are separated by a special
141 record. For ASCII files the first character must be flag
142 [Default is '>']. For binary files all fields must be NaN and
143 -b must set the number of output columns explicitly. By default
144 the -m setting applies to both input and output. Use -mi and
145 -mo to give separate settings to input and output.
146
148 To backtrack the (x,y,t) points in the file seamounts.d to their origin
149 (presumably the hotspot), using the DC85.d Euler poles, run
150 backtracker seamounts.d -Db -EDC85.d > newpos.d
152 To project flowlines forward from the (x,y,t) points stored in several
154 3-column, binary, double precision files, run
155 backtracker points.* -Df -EDC85.d -Lf25 -bo -bi3 > lines.b
157 This file can then be plotted with psxy -M.
159 To compute the predicted Hawaiian hotspot track from 0 to 80 Ma every 1
161 Ma, given a history of hotspot motion file (HIdrift.txt) and a set of
162 total reconstruction rotations for the plate (PAC_APM.d), try
163 echo 204 19 80 | backtracker -Df -C -EPAC_APM.d -Lb1 > path.d
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167 Data coordinates are assumed to be geodetic and will automatically be
168 converted to geocentric before spherical rotations are performed. We
169 convert back to geodetic coordinates for output. Note: If your data
170 already are geocentric, you can avoid the conversion by using --ELLIP‐
171 SOID=sphere.
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174 GMT(1), project(1), grdrotater(1), grdspotter(1), mapproject(1),
175 hotspotter(1), originator(1)
176
178 Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80
179 (29), p. 319.
180GMT 4.5.6 10 Mar 2011 BACKTRACKER(1)