Ubuntu Manpage: x2sys_cross - Find and compute crossover errors

NAME

       x2sys_cross - Find and compute crossover errors

SYNOPSIS

       x2sys_cross track(s) -TTAG [ -Il|a|c ] [ -Jparameters ] [ -Kcombi.lis ] [ -L ] [ -Qe|i ] [ -Sl|u|hspeed ]
       [ -V ] [ -Wsize ] [ -2 ] [ -bo[s|S|d|D[ncol]|c[var1/...]] ]

DESCRIPTION

x2sys_cross is used to determine all intersections between ("external cross-overs") or within ("internal
cross-overs") tracks (Cartesian or geographic), and report the time, position, distance along track,
heading and speed along each track segment, and the crossover error (COE) and mean values for all
observables. The names of the tracks are passed on the command line. By default, x2sys_cross will look
for both external and internal COEs. As an option, you may choose to project all data using one of the
map-projections prior to calculating the COE.

tracks Can be one or more ASCII, native binary, or COARDS netCDF 1-D data files. To supply the data
files via a text file with a list of tracks (one per record), specify the name of the track list
after a leading equal-sign (e.g., =tracks.lis). If the names are missing their file extension we
will append the suffix specified for this TAG. Track files will be searched for first in the
current directory and second in all directories listed in $X2SYS_HOME/TAG/TAG_paths.txt (if it
exists). [If $X2SYS_HOME is not set it will default to $GMT_SHAREDIR/x2sys]. (Note: MGD77 files
will also be looked for via MGD77_HOME/mgd77_paths.txt and *.gmt files will be searched for via
$GMT_SHAREDIR/mgg/gmtfile_paths).

-T Specify the x2sys TAG which tracks the attributes of this data type.

OPTIONS

       No space between the option flag and the associated arguments.

       -I     Sets the interpolation mode for estimating values at the crossover. Choose among:
              l Linear interpolation [Default].
              a Akima spline interpolation.
              c Cubic spline interpolation.

       -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 setting in .gmtdefaults4, but this can be
              overridden on the command line by appending c, i, or m to the  scale/width  value.   When  central
              meridian  is  optional,  default  is  center  of  longitude  range on -R option.  Default standard
              parallel is the equator.  For map height, max dimension, or min dimension, append h, +,  or  -  to
              the width, respectively.
              More details can be found in the psbasemap man pages.

              CYLINDRICAL PROJECTIONS:

              -Jclon0/lat0/scale (Cassini)
              -Jcyl_stere/[lon0/[lat0/]]scale (Cylindrical Stereographic)
              -Jj[lon0/]scale (Miller)
              -Jm[lon0/[lat0/]]scale (Mercator)
              -Jmlon0/lat0/scale (Mercator - Give meridian and standard parallel)
              -Jo[a]lon0/lat0/azimuth/scale (Oblique Mercator - point and azimuth)
              -Jo[b]lon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
              -Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point and pole)
              -Jq[lon0/[lat0/]]scale (Cylindrical Equidistant)
              -Jtlon0/[lat0/]scale (TM - Transverse Mercator)
              -Juzone/scale (UTM - Universal Transverse Mercator)
              -Jy[lon0/[lat0/]]scale (Cylindrical Equal-Area)

              CONIC PROJECTIONS:

              -Jblon0/lat0/lat1/lat2/scale (Albers)
              -Jdlon0/lat0/lat1/lat2/scale (Conic Equidistant)
              -Jllon0/lat0/lat1/lat2/scale (Lambert Conic Conformal)
              -Jpoly/[lon0/[lat0/]]scale ((American) Polyconic)

              AZIMUTHAL PROJECTIONS:

              -Jalon0/lat0[/horizon]/scale (Lambert Azimuthal Equal-Area)
              -Jelon0/lat0[/horizon]/scale (Azimuthal Equidistant)
              -Jflon0/lat0[/horizon]/scale (Gnomonic)
              -Jglon0/lat0[/horizon]/scale (Orthographic)
              -Jglon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale (General Perspective).
              -Jslon0/lat0[/horizon]/scale (General Stereographic)

              MISCELLANEOUS PROJECTIONS:

              -Jh[lon0/]scale (Hammer)
              -Ji[lon0/]scale (Sinusoidal)
              -Jkf[lon0/]scale (Eckert IV)
              -Jk[s][lon0/]scale (Eckert VI)
              -Jn[lon0/]scale (Robinson)
              -Jr[lon0/]scale (Winkel Tripel)
              -Jv[lon0/]scale (Van der Grinten)
              -Jw[lon0/]scale (Mollweide)

              NON-GEOGRAPHICAL PROJECTIONS:

              -Jp[a]scale[/origin][r|z] (Polar coordinates (theta,r))
              -Jxx-scale[d|l|ppow|t|T][/y-scale[d|l|ppow|t|T]] (Linear, log, and power scaling)

       -K     Only  process  the  pair-combinations  found  in  the file combi.lis [Default process all possible
              combinations among the specified files].

       -L     Output results using the old XOVER format [Default is x2sys format].  This option should  only  be
              used  with  *.gmt-formatted  MGD77  files.   See  the GMT mgg supplement for file description; see
              Wessel [1989] for details on the XOVER format.

       -Q     Append e for external COEs only, and i for internal COEs only [Default is all COEs].

       -R     west, east, south, and north specify the Region of interest, and you may specify them  in  decimal
              degrees  or  in  [+-]dd:mm[:ss.xxx][W|E|S|N]  format.   Append r if lower left and upper right map
              coordinates are given instead of w/e/s/n.  The two shorthands -Rg and -Rd stand for global  domain
              (0/360  and -180/+180 in longitude respectively, with -90/+90 in latitude). Alternatively, specify
              the name of an existing grid file and the -R settings (and grid spacing, if applicable) are copied
              from the grid.  For Cartesian data just give xmin/xmax/ymin/ymax.  This option limits the COEs  to
              those that fall inside the specified domain.

       -S     Defines  window  of  track  speeds.   If speeds are outside this window we do not calculate a COE.
              Specify
                   -Sl sets lower speed [Default is 0].
                   -Su sets upper speed [Default is Infinity].
                   -Sh does not limit the speed but sets a lower speed below which headings will not be computed
              (i.e., set to NaN) [Default calculates headings regardless of speed].

       -V     Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].

       -W     Give the maximum number of data points on either side of  the  crossover  to  use  in  the  spline
              interpolation [3].

       -2     Report the values of each track at the crossover [Default reports the crossover value and the mean
              value].

       -bo    Selects  binary  output.  Append s for single precision [Default is d (double)].  Uppercase S or D
              will force byte-swapping.  Optionally, append ncol, the number of desired columns in  your  binary
              output file.

REMARKS

       The  COEs  found  are  printed out to standard output in ASCII format (unless -bo is set).  When ASCII is
       chosen, the output format depends on whether or not old-style XOVER output (-L) has  been  selected  [See
       the  x_over  man  page  for  more details].  If ASCII, then the first record contains the name of the tag
       used, the second records specifies the exact command line  used  for  this  run,  and  the  third  record
       contains  the  names  of  each  column.   For each track pair, there will be a multisegment header record
       containing the two file names and their start/stop/dist information (start/stop is absolute time  or  NaN
       if  unavailable  while dist is the total track length), whereas subsequent records have the data for each
       COE encountered.  The fields written out are x, y, time along track #1 and #2, distance  along  track  #1
       and #2, heading along track #1 and #2, velocity along track #1 and #2, and then pairs of columns for each
       selected  observable.  These are either pairs of (COE, average value) for each data type (or track-values
       #1 and #2; see -2).  It is recommended 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.

SIGN CONVENTION

       If track_a and track_b are passed on the command line, then the COE value  is  Value  (track_a)  -  Value
       (track_b).

PRECISION AND FORMAT

       The  output  format  of  individual  columns are controlled by D_FORMAT except for geographic coordinates
       (OUTPUT_DEGREE_FORMAT) and absolute calendar time (OUTPUT_DATE_FORMAT, OUTPUT_CLOCK_FORMAT).   Make  sure
       these are set to give you enough significant digits to achieve the desired precision.

EXAMPLES

       To  compute  all  internal  crossovers  in  the gmt-formatted file c2104.gmt, and output in the old XOVER
       format, using the tag GMT, try

       x2sys_cross c2104.gmt -L -T GMT > c2104.d

       To  find  the  crossover  locations  with  bathymetry  between  the  two  MGD77  files  A13232.mgd77  and
       A99938.mgd77, using the MGD77 tag, try

       x2sys_cross A13232.mgd77 A99938.mgd77 -Qe -T MGD77 > crossovers.d

REFERENCES

       Wessel,  P.  (2010),  Tools  for  analyzing  intersecting  tracks:  the  x2sys  package. IT(Computers and
       Geosciences), BD(36), 348-354.
       Wessel, P. (1989), XOVER: A cross-over error detector for track data, Computers and  Geosciences,  15(3),
       333-346.