Provided by: gmt-common_5.4.5+dfsg-1_all bug

NAME

       backtracker - Generate forward and backward flowlines and hotspot tracks

SYNOPSIS

       backtracker  [  table  ]   -Erot_file|lon/lat/angle  [   -A[young/old]  ]  [   -Df|b  ]  [
       -Fdrift.txt ] [  -Lf|b[step] ] [  -Nupper_age  ]  [   -Qfixed_age  ]  [   -Sfilestem  ]  [
       -Tzero_age  ]  [   -V[level]  ]  [   -W[a|t]  ]  [  -bbinary ] [ -dnodata ] [ -eregexp ] [
       -hheaders ] [ -iflags ] [ -oflags ] [ -:[i|o] ]

       Note: No space is allowed between the option flag and the associated arguments.

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.

REQUIRED ARGUMENTS

       -Erotfile
              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 tstop is not present in
              the record then a total reconstruction rotation is expected and tstop is implicitly
              set  to  0  and  should  not  be specified for any of the records 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. You may prepend a leading  +
              to  the filename to indicate you wish to invert the rotations.  Alternative 1: Give
              the filename composed of two plate IDs separated by a hyphen (e.g., PAC-MBL) and we
              will instead extract that rotation from the GPlates rotation database. We return an
              error if the rotation cannot be found.  Alternative 2: Specify lon/lat/angle, i.e.,
              the  longitude, latitude, and opening angle (all in degrees and separated by /) for
              a single total reconstruction rotation.

OPTIONAL ARGUMENTS

       table  One or more ASCII (or binary, see -bi[ncols][type]) data table  file(s)  holding  a
              number of data columns. If no tables are given then we read from standard input.

       -A[young/old]
              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.

       -Df|b  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.

       -Fdrift.txt
              Supply a file with lon, lat, age records  that  describe  the  history  of  hotspot
              motion  for  the  current  hotspot.  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].

       -Lf|b[step]
              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 or not provided 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.

       -Nupper_age
              Set the maximum age to extend the oldest stage rotation back in time [Default is no
              extension].

       -Qfixed_age
              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.

       -Sfilestem
              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.

       -Tzero_age
              Set the current time [Default is 0 Ma].

       -V[level] (more ...)
              Select verbosity level [c].

       -W[a|t]
              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 total reconstruction 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.

       -bi[ncols][t] (more ...)
              Select native binary input. [Default is 3 input columns].

       -bo[ncols][type] (more ...)
              Select native binary output. [Default is same as input].

       -d[i|o]nodata (more ...)
              Replace input columns that equal nodata with NaN and do the reverse on output.

       -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
              Only accept data records that match the given pattern.

       -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
              Skip or produce header record(s).

       -icols[+l][+sscale][+ooffset][,...] (more ...)
              Select input columns and transformations (0 is first column).

       -ocols[,...] (more ...)
              Select output columns (0 is first column).

       -:[i|o] (more ...)
              Swap 1st and 2nd column on input and/or output.

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows
              just use -).

       -+ or just +
              Print  an  extensive  usage  (help)  message,  including  the  explanation  of  any
              module-specific option (but not the GMT common options), then exits.

       -? or no arguments
              Print  a  complete  usage (help) message, including the explanation of all options,
              then exits.

GEODETIC VERSUS GEOCENTRIC COORDIINATES

       All spherical rotations are applied to geocentric coordinates.  This means  that  incoming
       data  points  and grids are considered to represent geodetic coordinates and must first be
       converted  to  geocentric  coordinates.  Rotations  are  then  applied,  and   the   final
       reconstructed  points  are  converted back to geodetic coordinates.  This default behavior
       can be bypassed if the ellipsoid setting PROJ_ELLIPSOID is changed to Sphere.

EXAMPLES

       To backtrack the (x,y,t) points in the file seamounts.txt to their origin (presumably  the
       hotspot), using the DC85.txt Euler poles, run

              gmt backtracker seamounts.txt -Db -EDC85.txt > newpos.txt

       To  project  flowlines forward from the (x,y,t) points stored in several 3-column, binary,
       double precision files, run

              gmt backtracker points.\* -Df -EDC85.txt -Lf25 -bo -bi3 > lines.b

       This file can then be plotted with psxy.  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.txt), try

              echo 204 19 80 | gmt backtracker -Df -EPAC_APM.txt -Lb1 > path.txt

NOTES

       GMT distributes the EarthByte rotation model Global_EarthByte_230-0Ma_GK07_AREPS.rot.   To
       use an alternate rotation file, create an environmental parameters named GPLATES_ROTATIONS
       that points to an alternate rotation file.

SEE ALSO

       gmt  ,  gmtpmodeler,  grdpmodeler,   grdrotater,   grdspotter,   hotspotter,   mapproject,
       originator, project, psxy

REFERENCES

       Wessel, P., 1999, "Hotspotting" tools released, EOS Trans. AGU, 80 (29), p. 319.

COPYRIGHT

       2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe