## 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][n] ] [ -2 ]

## DESCRIPTION

           x2sys_cross is used to determine all intersections between
           or  within tracks, and report the time, position, discrep
           ancies in all observables, the mean values of the  observ
           ables,  heading along each track segment, 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 calcula
                  tion:
                          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 dis
                  continuity 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 MEA
                  SURE_UNIT setting 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  ori
                  gin)
                  -Jmlon0/lat0/scale  (Mercator  -  Give meridian and
                  standard 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 Equa
                  tor as y = 0)
                  -Jtlon0/lat0/scale  (TM  - Transverse Mercator, set
                  origin)
                  -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/[slat/]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 man
                  pages.

           -K     Only process the  pair-combinations  found  in  the
                  file combi.lis [Default process all possible combi
                  nations  among  the  specified  files].    Suitable
                  option for passing old x_setup output.

           -N     Maximum  number  of points to use in the interpola
                  tion [6].

           -O     Output results using the old XOVER format  [Default
                  is  X2SYS format].  This option 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 min
                  utes [and  seconds],  use  the  dd:mm[:ss]  format.
                  Append  r if lower left and upper right map coordi
                  nates are given instead of wesn.

           -S     Defines window of track speed within which to  cal
                  culate 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 Infinity].

           -X     Append  e  for  external crossovers only, and i for
                  internal   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 preci
                  sion [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  out
           put  (-O) has been selected.  If so, then the first record
           contains the file names and their start year, whereas sub
           sequent  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. 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 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 sen
           sitive to outliers that tend to  introduce  wild  oscilla
           tions in the interpolation.

## 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)

                                1 Mar 2002             X2SYS_CROSS(l)