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