Provided by: gmt-common_5.2.1+dfsg-3build1_all bug

NAME

       backtracker - Generate forward and backward flowlines and hotspot tracks

SYNOPSIS

       backtracker  [  table  ]  rot_file|lon/lat/angle  [  [young/old] ] [ f|b ] [ drift.txt ] [
       f|bstep ] [ upper_age ] [ fixed_age ] [ filestem ] [ zero_age ] [ [level] ] [  [a|t]  ]  [
       -b<binary> ] [ -d<nodata> ] [ -h<headers> ] [ -i<flags> ] [ -o<flags> ] [ -:[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|bstep
              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 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.

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

       -icols[l][sscale][ooffset][,...] (more ...)
              Select input columns (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
              use just -).

       -+ 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  options,  then
              exits.

       --version
              Print GMT version and exit.

       --show-datadir
              Print full path to GMT share directory and exit.

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.gmt \* -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 , project , grdrotater, grdspotter, mapproject, hotspotter, originator

REFERENCES

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

COPYRIGHT

       2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe