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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