X_UPDATE(1gmt) Generic Mapping Tools X_UPDATE(1gmt)NAME
x_update - Archiving of Cross-Over Information
SYNOPSIS
x_update cross-overfile [ -Xxbase ] [ -Llegbase ] [ -V ] [ -Wmax ]
DESCRIPTION
x_update reads the ASCII file produced by x_over and writes the information to the database files xx_base.b and xx_legs.b (unless other
filenames are specified on the command line) using a compact, binary format. The options recognized are:
-X Indicate alternate xx_base.b file.
-L Indicate alternate xx_legs.b file.
-V Selects verbose mode, which will send progress reports to stderr [Default runs "silently"]. Reports the pair currently being pro-
cessed.
-W Prints a warning if the number of COEs generated by any pair of legs exceed max.
BEWARE
For security reasons the xx_legs.b are first renamed to xx_legs.b_old, to prevent loss of information if a black-out or system crash should
occur during writing of the new xx_legs.b file. It is recommended that the old file is left on the disk in case of other disasters. Note
that x_update does not check if a pair of legs already exist in the xx_base.b file. It is the user's responsibility to ensure that duplica-
tion of information does not occur. Should some pairs already in the database need to be re-examined, then run x_remove which will wipe out
all traces of the specified cruises from the x_system data base files. Now we can pass the pairs that need to be redone through
x_over/x_update again.
SEE ALSO GMT(1), x_system(1)REFERENCES
Wessel, P. XOVER: A Cross-over Error Detector for Track Data, Computers & Geosciences, 15, 333-346.
GMT 4.5.7 15 Jul 2011 X_UPDATE(1gmt)
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X_OVER(1gmt) Generic Mapping Tools X_OVER(1gmt)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/magnetics/ba-
thymetry, 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 an Akima 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 Selects verbose mode, which will send progress reports to stderr [Default runs "silently"]. Report the number of cross-overs for
this pair of legs.
BEWARE
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 rec-
ommended that the Akima spline is used instead of the natural cubic spline, since it is less sensitive to outliers that tend to introduce
wild oscillations in the interpolation.
SEE ALSO GMT(1), x_system(1)REFERENCES
Wessel, P. XOVER: A Cross-over Error Detector for Track Data, Computers & Geosciences, 15, 333-346.
GMT 4.5.7 15 Jul 2011 X_OVER(1gmt)