NAME
x2sys_cross - Find and compute Cross-Over Errors
SYNOPSIS
x2sys_cross file(s) OR -Lflist [ -Agap ] [ -Cc|f|g ] [
-Ddeffile ] [ -Fflags ] [ -Gd|g ] [ -Jparams ] [-Kcombi.lis]
[ -Nwindow ] [ -O ] [ -Sl|uspeed ] [ -Tl|a|c ] [ -Wsize ] [
-V ] [ -Xe|i ] [ -bo[s] ] [ -2 ]
DESCRIPTION
x2sys_cross is used to determine all intersections between
or within tracks, and report the time, position, discrepan-
cies in all observables, the mean values of the observables,
heading along each tracksegment, and the distance along
track at the cross-over point. The names of the files are
passed on the command line, or as a list of files with the
-L option. If they are identical or only one name is
passed, then x2sys_cross will also look for internal cross-
overs. The optional parameters are:
-A Ignore crossovers on segments of length > gap [no gap
checking].
-C Select procedure for along-track distance calculation:
c Cartesian distances [Default].
f Flat earth distances.
g Great circle distances.
-D Give the definition file for this data format [x2sys].
-F Sets which columns to use. Give a comma-separated list
of column names [Default is all columns].
-G Selects geographical coordinates. Append d for discon-
tinuity at the Dateline (makes longitude go from -180
to + 180) or g for discontinuity at Greenwhich (makes
longitude go from 0 to 360 [Default]).
-J Selects the map projection. Scale is UNIT/degree,
1:xxxxx, or width in UNIT (upper case modifier). UNIT
is cm, inch, or m, depending on the MEASURE_UNIT set-
ting in .gmtdefaults, but this can be overridden on the
command line by appending the c, i, or m to the
scale/width value.
CYLINDRICAL PROJECTIONS:
-Jclon0/lat0/scale (Cassini)
-Jjlon0/scale (Miller)
-Jmscale (Mercator - Greenwich and Equator as origin)
-Jmlon0/lat0/scale (Mercator - Give meridian and stan-
dard parallel)
-Joalon0/lat0/azimuth/scale (Oblique Mercator - point
and azimuth)
-Joblon0/lat0/lon1/lat1/scale (Oblique Mercator - two
points)
-Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point
and pole)
-Jqlon0/scale (Equidistant Cylindrical Projection
(Plate Carree))
-Jtlon0/scale (TM - Transverse Mercator, with Equator
as y = 0)
-Jtlon0/lat0/scale (TM - Transverse Mercator, set ori-
gin)
-Juzone/scale (UTM - Universal Transverse Mercator)
-Jylon0/lats/scale (Basic Cylindrical Projection)
AZIMUTHAL PROJECTIONS:
-Jalon0/lat0/scale (Lambert).
-Jelon0/lat0/scale (Equidistant).
-Jflon0/lat0/horizon/scale (Gnomonic).
-Jglon0/lat0/scale (Orthographic).
-Jslon0/lat0/scale (General Stereographic)
CONIC PROJECTIONS:
-Jblon0/lat0/lat1/lat2/scale (Albers)
-Jdlon0/lat0/lat1/lat2/scale (Equidistant)
-Jllon0/lat0/lat1/lat2/scale (Lambert)
MISCELLANEOUS PROJECTIONS:
-Jhlon0/scale (Hammer)
-Jilon0/scale (Sinusoidal)
-Jk[f|s]lon0/scale (Eckert IV (f) and VI (s))
-Jnlon0/scale (Robinson)
-Jrlon0/scale (Winkel Tripel)
-Jvlon0/scale (Van der Grinten)
-Jwlon0/scale (Mollweide)
NON-GEOGRAPHICAL PROJECTIONS:
-Jp[a]scale[/origin] (polar (theta,r) coordinates,
optional a for azimuths and offset theta [0])
-Jxx-scale[l|ppow][/y-scale[l|ppow]] (Linear, log, and
power scaling)
More details can be found in the psbasemap manpages.
-K Only process the pair-combinations found in the file
combi.lis [Default process all possible combinations
among the specified files]. Suitable option for pass-
ing old x_setup output.
-N Maximum number of points to use in the interpolation
[6].
-O Output results using the old XOVER format [Default is
X2SYS format]. This options should only be used with
*.gmt-formatted MGD77 files.
-R west, east, south, and north specify the Region of
interest. To specify boundaries in degrees and minutes
[and seconds], use the dd:mm[:ss] format. Append r if
lower left and upper right map coordinates are given
instead of wesn.
-S Defines window of track speed within which to calculate
crossovers.
-Sl sets lower speed [Default is 0].
-Su sets upper speed [Default is Infinity].
-T Sets the interpolation mode. Choose among:
l Linear interpolation [Default].
a Akima spline interpolation.
c Cubic spline interpolation.
-V Selects verbose mode, which will send progress reports
to stderr [Default runs "silently"].
-W Sets maximum time gap (in user units) allowed between
points on either side of a crossover [Default is Infin-
ity].
-X Append e for external crossovers only, and i for inter-
nal crossovers only [Default is all crossovers].
-2 Report the values of each track at the crossover
[Default is the crossover value and the mean value].
-bo Selects binary output. Append s for single precision
[Default is double].
REMARKS
The COEs found are printed out to standard output in ASCII
format (unless -bo is set). When ASCII is chosen, the out-
put format depends on whether or not old-style XOVER output
(-O) has been selected. If so, then the first record con-
tains the file names and their start year, whereas subse-
quent 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, aver-
age gravity, average magnetics, average bathymetry, heading
along track #1, and heading along track #2. If the default
format is chosen then the header record starts with "> ",
and the output format for crossovers are first 8 columns
that contain x, y, time along track #1, time along track #2,
distance along track #1, distance along track #2, heading
along track #1, and heading along track #2, and then pairs
of (COE, average value) for each data type. Sign conven-
tion: If lega and legb are passed on the command line, then
the COE value is Value (lega) - Value (legb). It is recom-
mended 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.
EXAMPLES
To compute all internal crossovers in the gmt-formatted file
c2104.gmt, and output in the old XOVER format, use
x2sys_cross c2104.gmt -O -Dgmt > c2104.d
To find the crossover locations with bathymetry between the
two MGD77 files A13232.mgd77 and A99938.mgd77, try
x2sys_cross A13232.mgd77 A99938.mgd77 -Xe -Dmgd77
-Flon,lat,top > crossovers.d
SEE ALSO
gmt(l), x2sys_datalist(l)