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.