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.