NAME

       x_over - Find and compute Cross-Over Errors


SYNOPSIS

       x_over  leg_1  [  leg_2  ]  [ -A ] [ -C ] [ -L ] [ -V ] [ -Wtimegap ] [
       -Gfact ] [ -Mfact ] [ -Tfact ] [ -Nnp_int ]


DESCRIPTION

       x_over is used to inspect two cruises to see if they intersect, and  if
       so   report   the  time,  position,  discrepancies  in  gravity/magnet-
       ics/bathymetry, heading for each track segment, 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 x_over 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 magnetics, 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 oscillations in the interpola-
       tion. A version of x_over compiled for a SUN with FPA board is provided
       (x_over).


SEE ALSO

       gmt(GMTMANSECTION), x_system(GMTMANSECTION)


REFERENCES

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



                                  1 Jan 2004                         x_over(l)

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