NAME

     XOVER - Find and compute Cross-Over Errors


SYNOPSIS

     xover leg_1 [ leg_2 ] [ -A ] [ -C ] [ -L ] [ -V ] [  -Wtime-
     gap ] [ -Gfact ] [ -Mfact ] [ -Tfact ] [ -Nnp_int ]


DESCRIPTION

     xover is used to inspect two cruises to see if  they  inter-
     sect,  and if so report the time, position, discrepancies in
     gravity/magnetics/bathymetry, heading for each tracksegment,
     and the average values of the geophysical observables at the
     cross-over point. The names of the legs are  passed  on  the
     command  line.  If  they  are  identical or only one name is
     passed, then  xover  looks  for  internal  cross-overs.  The
     optional parameters are:

     -A   Use Akima's spline to interpolate the geophysical field
          at the cross-over point.

     -C   Use a Natural Cubic spline function instead.

     -L   Use a linear interpolant [Default].

     -W   Do not compute cross-overs if the 2 nearest points  are
          more than timegap minutes apart.

     -G   Scale gravity by fact [Default is 0.1  since  gmt-files
          store gravity in g.u.]

     -M   Scale magnetic anomaly by fact [1.0].

     -T   Scale bathymetry by fact [1.0].

     -N   Specify how many points to  use  in  the  interpolation
          [Default is 6].

     -V   Verbose, report the number of cross-overs for this pair
          of legs.


     The COEs found are printed out to standard output  in  ASCII
     format.  The  first  record contains the leg names and their
     start year, whereas subsequent records  have  the  data  for
     each  COE  encountered. The fields written out are lat, lon,
     time  along  track  #1,  time  along  track  #2,  x_gravity,
     x_magnetics,  x_bathymetry, average gravity, average magnet-
     ics, average bathymetry, heading along track #1, and heading
     along track #2. Sign convention: If lega and legb are passed
     on the command line, then the COE value is  Value  (lega)  -
     Value  (legb).  It is recommended that the Akima's spline is
     used instead of the natural cubic spline, since it  is  less
     sensitive  to  outliers that tend to introduce wild oscilla-
     tions in the interpolation.  A version of xover compiled for
     a SUN with FPA board is provided (xover_fpa).


SEE ALSO

     gmt(l), x_system(l)


REFERENCES

     Wessel, P. XOVER: A  Cross-over  Error  Detector  for  Track
     Data, Computers & Geosciences, 15, 333-346.