1X_OVER(1)                    Generic Mapping Tools                   X_OVER(1)
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NAME

6       x_over - Find and compute Cross-Over Errors
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SYNOPSIS

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

13       x_over is used to inspect two cruises to see if they intersect, and  if
14       so  report  the  time, position, discrepancies in gravity/magnetics/ba‐
15       thymetry, heading for each track segment, and the average values of the
16       geophysical  observables at the cross-over point. The names of the legs
17       are passed on the command line. If they are identical or only one  name
18       is  passed,  then  x_over  looks for internal cross-overs. The optional
19       parameters are:
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21       -A     Use an Akima spline to interpolate the geophysical field at  the
22              cross-over point.
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24       -C     Use a Natural Cubic spline function instead.
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26       -L     Use a linear interpolant [Default].
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28       -W     Do not compute cross-overs if the 2 nearest points are more than
29              timegap minutes apart.
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31       -G     Scale gravity by fact [Default  is  0.1  since  gmt-files  store
32              gravity in g.u.]
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34       -M     Scale magnetic anomaly by fact [1.0].
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36       -T     Scale bathymetry by fact [1.0].
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38       -N     Specify  how many points to use in the interpolation [Default is
39              6].
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41       -V     Verbose, report the number of cross-overs for this pair of legs.
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BEWARE

44       The COEs found are printed out to standard output in ASCII format.  The
45       first  record contains the leg names and their start year, whereas sub‐
46       sequent records have the data for  each  COE  encountered.  The  fields
47       written  out  are  lat,  lon, time along track #1, time along track #2,
48       x_gravity, x_magnetics, x_bathymetry, average gravity, average  magnet‐
49       ics,  average  bathymetry,  heading  along  track #1, and heading along
50       track #2. Sign convention: If lega and legb are passed on  the  command
51       line,  then the COE value is Value (lega) - Value (legb).  It is recom‐
52       mended that the Akima spline is  used  instead  of  the  natural  cubic
53       spline,  since  it is less sensitive to outliers that tend to introduce
54       wild oscillations in the interpolation.
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SEE ALSO

57       GMT(1), x_system(1)
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REFERENCES

60       Wessel, P. XOVER: A Cross-over Error Detector for Track Data, Computers
61       & Geosciences, 15, 333-346.
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65GMT 4.3.1                         15 May 2008                        X_OVER(1)