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x2sys_cross(1)                        GMT                       x2sys_cross(1)




NAME

       x2sys_cross - Calculate crossovers between track data files


SYNOPSIS

       x2sys_cross  track(s)   -TTAG  [   -Acombi.lis  ]  [   -C[runtimes] ] [
       -Il|a|c ] [  -Jparameters ] [  -Qe|i ] [  -Sl|u|hspeed ] [  -V[level] ]
       [  -Wsize ] [  -Z ] [ -bobinary ] [ -donodata ]

       Note:  No  space  is allowed between the option flag and the associated
       arguments.


DESCRIPTION

       x2sys_cross is used to determine all intersections  between  (aexternal
       cross-oversa)  or  within (ainternal cross-oversa) tracks (Cartesian or
       geographic), and report the time, position, distance along track, head-
       ing  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 exter-
       nal and internal COEs. As an option, you may choose to project all data
       using one of the map-projections prior to calculating the COE.


REQUIRED ARGUMENTS

       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 cur-
              rent   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/gmt-
              file_paths).

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


OPTIONAL ARGUMENTS

       -Acombi.lis
              Only  process  the pair-combinations found in the file combi.lis
              [Default process all possible combinations among  the  specified
              files]. The file combi.lis created by x2sys_get -L option

       -C[runtimes]
              Compute  and append the processing run-time for each pair to the
              progress message. Append a filename to save these  run-times  to
              file.   The  idea  here  is to use the knowledge of run-times to
              split the main process in a number  of  sub-processes  that  can
              each  be  launched  in  a different processor of your multi-core
              machine. See the MATLAB function split_file4coes.m that lives in
              the x2sys supplement source code.

       -Il|a|c
              Sets  the  interpolation  mode  for  estimating  values  at  the
              crossover.  Choose among:

              l Linear interpolation [Default].

              a Akima spline interpolation.

              c Cubic spline interpolation.

       -Jparameters (more a|)
              Select map projection.

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

       -Rwest/east/south/north[/zmin/zmax][+r][+uunit]
              west, east, south, and north specify the region of interest, and
              you   may   specify   them   in   decimal    degrees    or    in
              [A+-]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  for grid creation, give Rcodelon/lat/nx/ny, where
              code is a 2-character combination of L, C, R (for left,  center,
              or  right)  and T, M, B for top, middle, or bottom. e.g., BL for
              lower left.  This indicates which point on a rectangular  region
              the lon/lat coordinate refers to, and the grid dimensions nx and
              ny with grid spacings via -I is used to create the corresponding
              region.   Alternatively,  specify  the  name of an existing grid
              file and the -R settings (and grid spacing, if  applicable)  are
              copied from the grid. Appending +uunit expects projected (Carte-
              sian) coordinates compatible with chosen  -J  and  we  inversely
              project  to determine actual rectangular geographic region.  For
              perspective view (-p), optionally append /zmin/zmax.  In case of
              perspective view (-p), a z-range (zmin, zmax) can be appended to
              indicate the third dimension. This needs to be  done  only  when
              using  the -Jz option, not when using only the -p option. In the
              latter case a perspective view of the plane is plotted, with  no
              third     dimension.    For    Cartesian    data    just    give
              xmin/xmax/ymin/ymax. This option limits the COEs to  those  that
              fall inside the specified domain.

       -Sl|u|hspeed
              Defines  window of track speeds. If speeds are outside this win-
              dow 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 calcu-
              lates headings regardless of speed].

       -V[level] (more a|)
              Select verbosity level [c].

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

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

       -bo[ncols][type] (more a|)
              Select native binary output.

       -donodata (more a|)
              Replace output columns that equal NaN with nodata.

       -^ or just -
              Print a short message about the  syntax  of  the  command,  then
              exits (NOTE: on Windows just use -).

       -+ or just +
              Print  an extensive usage (help) message, including the explana-
              tion of any module-specific  option  (but  not  the  GMT  common
              options), then exits.

       -? or no arguments
              Print a complete usage (help) message, including the explanation
              of all options, then exits.


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 con-
       tains 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  segment  header
       record containing the two file names and their start/stop/dist informa-
       tion (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 -Z). 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  FOR-
       MAT_FLOAT_OUT  except  for  geographic coordinates (FORMAT_GEO_OUT) and
       absolute calendar time (FORMAT_DATE_OUT, FORMAT_CLOCK_OUT).  Make  sure
       these  are  setto  give  you  enough  significant digits to achieve the
       desired precision.


EXAMPLES

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

              gmt x2sys_cross c2104.gmt -TGMT > c2104.d

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

              gmt x2sys_cross A13232.mgd77 A99938.mgd77 -Qe -TMGD77 > crossovers.d


REFERENCES

       Wessel, P. (2010), Tools for analyzing intersecting tracks:  the  x2sys
       package. Computers and Geosciences, 36, 348-354.

       Wessel,  P.  (1989), XOVER: A cross-over error detector for track data,
       Computers and Geosciences, 15(3), 333-346.


SEE ALSO

       gmt(1), x2sys_binlist(1), x2sys_init(1), x2sys_datalist(1),
       x2sys_get(1), x2sys_list(1), x2sys_put(1), x2sys_report(1),
       x2sys_solve(1), x_over


COPYRIGHT

       2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe



5.4.2                            Jun 24, 2017                   x2sys_cross(1)

gmt5 5.4.2 - Generated Thu Jun 29 18:03:50 CDT 2017
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