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)