## NAME

          backtracker - Forward and Backward flowlines and hotspot tracks

## SYNOPSIS

          backtracker [infile(s)] -Estage_file [ -Df|b ] [ -H[nrec] ] [ -Lf|tstep
          ] [ -Nupper_age ] [ -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) rotations.  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

          -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 position: -Lf
               will draw flowlines, while -Lb will draw backtrack (hotspot
               track) paths.  Append sampling interval in km.

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

          -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, project, mapproject, hotspotter

## REFERENCES

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