NAME

     backtracker - Forward and  Backward  flowlines  and  hotspot
     tracks


SYNOPSIS

     backtracker [infile(s)] -Estage_file [ -A[young/old] ] [  -C
     ]  [  -Df|b  ]  [ -H[nrec] ] [ -Lf|tstep ] [ -Nupper_age ] [
     -Sfilestem ] [ -Tzero_age ] [ -V ] [ -: ] [  -bi[s][n]  ]  [
     -bo[s] ]


DESCRIPTION

     backtracker reads (longitude, latitude, age) positions  from
     infiles  [or  standard input] and computes projected (x,y,t)
     coordinates using the specified  stage  pole  (Euler)  rota-
     tions.   You  can  either  calculate  just  final  positions
     [Default] or create a  sampled  track  between  initial  and
     final  position.   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 stage poles and  opening  angles.   This
          file  must  contain  one  record  for  each stage; each
          record must be of the following format:

               lon lat tstart tstop ccw-angle

          where time is in Ma and the rest is in degrees.  Oldest
          stage  must  be  listed first.  tstart is the time when
          the stage begins (oldest age).  Blank lines and records
          whose first column contains # will be ignored.


OPTIONS

     -A   Used in conjunction with -Lb|f to limit the track  out-
          put  to those sections whose predicted ages fit between
          the young and old limits.  If  -LB|F  is  used  instead
          then  the limits apply to the stage ids.  If not limits
          are supplied then individual limits for  each  seamount
          are expected in the input file's columns 4 and 5.

     -C   Expect Total Reconstruction Poles (Finite Poles) rather
          than  Backward  Stage  Poles  [Default]  File format is
          similar to the stage pole format  except  the  youngest
          rotation  must  be  listed  first  and  that the tstart
          column is optional (assumed to be 0 Ma).

     -D   Set the direction to go: -Df will go forward  in  time,
          while -Db will go backward in time [Default].

     -H   Input file(s) has Header record(s).  Number  of  header
          records  can  be  changed  by editing your .gmtdefaults
          file.  If used, GMT default is 1 header record.

     -L   Specify a sampled path between initial and final  posi-
          tion:  -Lf  will  draw  flowlines,  while -Lb will draw
          backtrack  (hotspot  track)  paths.   Append   sampling
          interval  in  km.   When  -LF or -LB is used, the third
          output column will contain the stage id (1 is youngest)
          [Default is along-track ages].

     -N   Set the maximum age to extend the oldest stage back  in
          time [no extension].

     -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.

     -T   Set the current time [0 Ma].

     -V   Selects verbose mode, which will send progress  reports
          to stderr [Default runs "silently"].

     -:   Toggles      between      (longitude,latitude)      and
          (latitude,longitude)    input/output.     [Default   is
          (longitude,latitude)].

     -bi  Selects binary input.  Append s  for  single  precision
          [Default  is  double].   Append  n  for  the  number of
          columns in the binary file(s).   [Default  is  3  input
          columns]

     -bo  Selects binary output.  Append s for  single  precision
          [Default is double].


EXAMPLES

     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.


SEE ALSO

     gmt(l),     project(l),     mapproject(l),     hotspotter(l)
     originator(l)


REFERENCES

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