1BACKTRACKER(1) GMT BACKTRACKER(1)
2
6 backtracker - Generate forward and backward flowlines and hotspot
7 tracks
8
10 backtracker [ table ] -Erot_file|lon/lat/angle [ -A[young/old] ] [
11 -Df|b ] [ -Fdrift.txt ] [ -Lf|b[step] ] [ -Nupper_age ] [
12 -Qfixed_age ] [ -Sfilestem ] [ -Tzero_age ] [ -V[level] ] [ -W[a|t]
13 ] [ -bbinary ] [ -dnodata ] [ -eregexp ] [ -hheaders ] [ -iflags ] [
14 -oflags ] [ -:[i|o] ]
15 Note: No space is allowed between the option flag and the associated
17 arguments.
18
20 backtracker reads (longitude, latitude, age) positions from infiles [or
21 standard input] and computes rotated (x,y,t) coordinates using the
22 specified rotation parameters. It can either calculate final positions
23 [Default] or create a sampled track (flowline or hotspot track) between
24 the initial and final positions. The former mode allows additional data
25 fields after the first 3 columns which must have (longitude,lati‐
26 tude,age). See option -: on how to read (latitude,longitude,age) files.
27
29 -Erotfile
30 Give file with rotation parameters. This file must contain one
31 record for each rotation; each record must be of the following
32 format:
33 lon lat tstart [tstop] angle [ khat a b c d e f g df ]
35 where tstart and tstop are in Myr and lon lat angle are in
37 degrees. tstart and tstop are the ages of the old and young ends
38 of a stage. If tstop is not present in the record then a total
39 reconstruction rotation is expected and tstop is implicitly set
40 to 0 and should not be specified for any of the records in the
41 file. If a covariance matrix C for the rotation is available it
42 must be specified in a format using the nine optional terms
43 listed in brackets. Here, C = (g/khat)*[ a b d; b c e; d e f ]
44 which shows C made up of three row vectors. If the degrees of
45 freedom (df) in fitting the rotation is 0 or not given it is set
46 to 10000. Blank lines and records whose first column contains #
47 will be ignored. You may prepend a leading + to the filename to
48 indicate you wish to invert the rotations. Alternative 1: Give
49 the filename composed of two plate IDs separated by a hyphen
50 (e.g., PAC-MBL) and we will instead extract that rotation from
51 the GPlates rotation database. We return an error if the rota‐
52 tion cannot be found. Alternative 2: Specify lon/lat/angle,
53 i.e., the longitude, latitude, and opening angle (all in degrees
54 and separated by /) for a single total reconstruction rotation.
55
57 table One or more ASCII (or binary, see -bi[ncols][type]) data table
58 file(s) holding a number of data columns. If no tables are given
59 then we read from standard input.
60 -A[young/old]
62 Used in conjunction with -Lb|f to limit the track output to
63 those sections whose predicted ages lie between the specified
64 young and old limits. If -LB|F is used instead then the limits
65 apply to the stage ids (id 1 is the youngest stage). If no lim‐
66 its are specified then individual limits for each record are
67 expected in columns 4 and 5 of the input file.
68 -Df|b Set the direction to go: -Df will go backward in time (from
70 younger to older positions), while -Db will go forward in time
71 (from older to younger positions) [Default]. Note: For -Db you
72 are specifying the age at the given location, whereas for -Df
73 you are not; instead you specify the age at the reconstructed
74 point.
75 -Fdrift.txt
77 Supply a file with lon, lat, age records that describe the his‐
78 tory of hotspot motion for the current hotspot. The reconstruc‐
79 tions will only use the 3rd data input column (i.e., the age) to
80 obtain the location of the hotspot at that time, via an interpo‐
81 lation of the hotspot motion history. This adjusted location is
82 then used to reconstruct the point or path [No drift].
83 -Lf|b[step]
85 Specify a sampled path between initial and final position: -Lf
86 will draw particle flowlines, while -Lb will draw backtrack
87 (hotspot track) paths. Append sampling interval in km. If step <
88 0 or not provided then only the rotation times will be returned.
89 When -LF or -LB is used, the third output column will contain
90 the stage id (1 is youngest) [Default is along-track predicted
91 ages]. You can control the direction of the paths by using -D.
92 -Nupper_age
94 Set the maximum age to extend the oldest stage rotation back in
95 time [Default is no extension].
96 -Qfixed_age
98 Assign a fixed age to all positions. Only lon, lat input is
99 expected [Default expects longitude, latitude, age]. Useful when
100 the input are points defining isochrons.
101 -Sfilestem
103 When -L is set, the tracks are normally written to stdout as a
104 multisegment file. Specify a filestem to have each track written
105 to filestem.#, where # is the track number. The track number is
106 also copied to the 4th output column.
107 -Tzero_age
109 Set the current time [Default is 0 Ma].
110 -V[level] (more ...)
112 Select verbosity level [c].
113 -W[a|t]
115 Rotates the given input (lon,lat,t) and calculates the confi‐
116 dence ellipse for the projected point. The input point must have
117 a time coordinate that exactly matches a particular total recon‐
118 struction rotation time, otherwise the point will be skipped.
119 Append t or a to output time or angle, respectively, after the
120 projected lon, lat. After these 2-3 items, we write azimuth,
121 major, minor (in km) for the 95% confidence ellipse. See -D for
122 the direction of rotation.
123 -bi[ncols][t] (more ...)
125 Select native binary input. [Default is 3 input columns].
126 -bo[ncols][type] (more ...)
128 Select native binary output. [Default is same as input].
129 -d[i|o]nodata (more ...)
131 Replace input columns that equal nodata with NaN and do the
132 reverse on output.
133 -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
135 Only accept data records that match the given pattern.
136 -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
138 Skip or produce header record(s).
139 -icols[+l][+sscale][+ooffset][,...] (more ...)
141 Select input columns and transformations (0 is first column).
142 -ocols[,...] (more ...)
144 Select output columns (0 is first column).
145 -:[i|o] (more ...)
147 Swap 1st and 2nd column on input and/or output.
148 -^ or just -
150 Print a short message about the syntax of the command, then
151 exits (NOTE: on Windows just use -).
152 -+ or just +
154 Print an extensive usage (help) message, including the explana‐
155 tion of any module-specific option (but not the GMT common
156 options), then exits.
157 -? or no arguments
159 Print a complete usage (help) message, including the explanation
160 of all options, then exits.
161
163 All spherical rotations are applied to geocentric coordinates. This
164 means that incoming data points and grids are considered to represent
165 geodetic coordinates and must first be converted to geocentric coordi‐
166 nates. Rotations are then applied, and the final reconstructed points
167 are converted back to geodetic coordinates. This default behavior can
168 be bypassed if the ellipsoid setting PROJ_ELLIPSOID is changed to
169 Sphere.
170
172 To backtrack the (x,y,t) points in the file seamounts.txt to their ori‐
173 gin (presumably the hotspot), using the DC85.txt Euler poles, run
174 gmt backtracker seamounts.txt -Db -EDC85.txt > newpos.txt
176 To project flowlines forward from the (x,y,t) points stored in several
178 3-column, binary, double precision files, run
179 gmt backtracker points.\* -Df -EDC85.txt -Lf25 -bo -bi3 > lines.b
181 This file can then be plotted with psxy. To compute the predicted
183 Hawaiian hotspot track from 0 to 80 Ma every 1 Ma, given a history of
184 hotspot motion file (HIdrift.txt) and a set of total reconstruction
185 rotations for the plate (PAC_APM.txt), try
186 echo 204 19 80 | gmt backtracker -Df -EPAC_APM.txt -Lb1 > path.txt
188
190 GMT distributes the EarthByte rotation model Global_Earth‐
191 Byte_230-0Ma_GK07_AREPS.rot. To use an alternate rotation file, create
192 an environmental parameters named GPLATES_ROTATIONS that points to an
193 alternate rotation file.
194
196 gmt , gmtpmodeler, grdpmodeler, grdrotater, grdspotter, hotspotter,
197 mapproject, originator, project, psxy
198
200 Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80
201 (29), p. 319.
202
204 2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
2055.4.5 Feb 24, 2019 BACKTRACKER(1)