1X2SYS_CROSS(1) GMT X2SYS_CROSS(1)
2
6 x2sys_cross - Calculate crossovers between track data files
7
9 x2sys_cross track(s) -TTAG [ -Acombi.lis ] [ -C[runtimes] ] [
10 -Il|a|c ] [ -Jparameters ] [ -Qe|i ] [ -Sl|u|hspeed ] [ -V[level] ]
11 [ -Wsize ] [ -Z ] [ -bobinary ] [ -donodata ]
12 Note: No space is allowed between the option flag and the associated
14 arguments.
15
17 x2sys_cross is used to determine all intersections between ("external
18 cross-overs") or within ("internal cross-overs") tracks (Cartesian or
19 geographic), and report the time, position, distance along track, head‐
20 ing and speed along each track segment, and the crossover error (COE)
21 and mean values for all observables. The names of the tracks are passed
22 on the command line. By default, x2sys_cross will look for both exter‐
23 nal and internal COEs. As an option, you may choose to project all data
24 using one of the map-projections prior to calculating the COE.
25
27 tracks Can be one or more ASCII, native binary, or COARDS netCDF 1-D
28 data files. To supply the data files via a text file with a list
29 of tracks (one per record), specify the name of the track list
30 after a leading equal-sign (e.g., =tracks.lis). If the names are
31 missing their file extension we will append the suffix specified
32 for this TAG. Track files will be searched for first in the cur‐
33 rent directory and second in all directories listed in
34 $X2SYS_HOME/TAG/TAG_paths.txt (if it exists). [If $X2SYS_HOME is
35 not set it will default to $GMT_SHAREDIR/x2sys]. (Note: MGD77
36 files will also be looked for via MGD77_HOME/mgd77_paths.txt and
37 *.gmt files will be searched for via $GMT_SHAREDIR/mgg/gmt‐
38 file_paths).
39 -TTAG Specify the x2sys TAG which tracks the attributes of this data
41 type.
42
44 -Acombi.lis
45 Only process the pair-combinations found in the file combi.lis
46 [Default process all possible combinations among the specified
47 files]. The file combi.lis created by x2sys_get -L option
48 -C[runtimes]
50 Compute and append the processing run-time for each pair to the
51 progress message. Append a filename to save these run-times to
52 file. The idea here is to use the knowledge of run-times to
53 split the main process in a number of sub-processes that can
54 each be launched in a different processor of your multi-core
55 machine. See the MATLAB function split_file4coes.m that lives in
56 the x2sys supplement source code.
57 -Il|a|c
59 Sets the interpolation mode for estimating values at the cross‐
60 over. Choose among:
61 l Linear interpolation [Default].
63 a Akima spline interpolation.
65 c Cubic spline interpolation.
67 -Jparameters (more ...)
69 Select map projection.
70 -Qe|i Append e for external COEs only, and i for internal COEs only
72 [Default is all COEs].
73 -Rwest/east/south/north[/zmin/zmax][+r][+uunit]
75 west, east, south, and north specify the region of interest, and
76 you may specify them in decimal degrees or in
77 [±]dd:mm[:ss.xxx][W|E|S|N] format Append +r if lower left and
78 upper right map coordinates are given instead of w/e/s/n. The
79 two shorthands -Rg and -Rd stand for global domain (0/360 and
80 -180/+180 in longitude respectively, with -90/+90 in latitude).
81 Alternatively for grid creation, give Rcodelon/lat/nx/ny, where
82 code is a 2-character combination of L, C, R (for left, center,
83 or right) and T, M, B for top, middle, or bottom. e.g., BL for
84 lower left. This indicates which point on a rectangular region
85 the lon/lat coordinate refers to, and the grid dimensions nx and
86 ny with grid spacings via -I is used to create the corresponding
87 region. Alternatively, specify the name of an existing grid
88 file and the -R settings (and grid spacing, if applicable) are
89 copied from the grid. Appending +uunit expects projected (Carte‐
90 sian) coordinates compatible with chosen -J and we inversely
91 project to determine actual rectangular geographic region. For
92 perspective view (-p), optionally append /zmin/zmax. In case of
93 perspective view (-p), a z-range (zmin, zmax) can be appended to
94 indicate the third dimension. This needs to be done only when
95 using the -Jz option, not when using only the -p option. In the
96 latter case a perspective view of the plane is plotted, with no
97 third dimension. For Cartesian data just give
98 xmin/xmax/ymin/ymax. This option limits the COEs to those that
99 fall inside the specified domain.
100 -Sl|u|hspeed
102 Defines window of track speeds. If speeds are outside this win‐
103 dow we do not calculate a COE. Specify
104 -Sl sets lower speed [Default is 0].
106 -Su sets upper speed [Default is Infinity].
108 -Sh does not limit the speed but sets a lower speed below which
110 headings will not be computed (i.e., set to NaN) [Default calcu‐
111 lates headings regardless of speed].
112 -V[level] (more ...)
114 Select verbosity level [c].
115 -Wsize Give the maximum number of data points on either side of the
117 crossover to use in the spline interpolation [3].
118 -Z Report the values of each track at the crossover [Default
120 reports the crossover value and the mean value].
121 -bo[ncols][type] (more ...)
123 Select native binary output.
124 -donodata (more ...)
126 Replace output columns that equal NaN with nodata.
127 -^ or just -
129 Print a short message about the syntax of the command, then
130 exits (NOTE: on Windows just use -).
131 -+ or just +
133 Print an extensive usage (help) message, including the explana‐
134 tion of any module-specific option (but not the GMT common
135 options), then exits.
136 -? or no arguments
138 Print a complete usage (help) message, including the explanation
139 of all options, then exits.
140
142 The COEs found are printed out to standard output in ASCII format
143 (unless -bo is set). When ASCII is chosen, the output format depends on
144 whether or not old-style XOVER output (-L) has been selected [See the
145 x_over man page for more details]. If ASCII, then the first record con‐
146 tains the name of the tag used, the second records specifies the exact
147 command line used for this run, and the third record contains the names
148 of each column. For each track pair, there will be a segment header
149 record containing the two file names and their start/stop/dist informa‐
150 tion (start/stop is absolute time or NaN if unavailable while dist is
151 the total track length), whereas subsequent records have the data for
152 each COE encountered. The fields written out are x, y, time along track
153 #1 and #2, distance along track #1 and #2, heading along track #1 and
154 #2, velocity along track #1 and #2, and then pairs of columns for each
155 selected observable. These are either pairs of (COE, average value) for
156 each data type (or track-values #1 and #2; see -Z). It is recommended
157 that the Akima spline is used instead of the natural cubic spline,
158 since it is less sensitive to outliers that tend to introduce wild
159 oscillations in the interpolation.
160
162 If track_a and track_b are passed on the command line, then the COE
163 value is Value (track_a) - Value (track_b).
164
166 The output format of individual columns are controlled by FOR‐
167 MAT_FLOAT_OUT except for geographic coordinates (FORMAT_GEO_OUT) and
168 absolute calendar time (FORMAT_DATE_OUT, FORMAT_CLOCK_OUT). Make sure
169 these are setto give you enough significant digits to achieve the
170 desired precision.
171
173 To compute all internal crossovers in the gmt-formatted file c2104.gmt,
174 and using the tag GMT, try
175 gmt x2sys_cross c2104.gmt -TGMT > c2104.d
177 To find the crossover locations with bathymetry between the two MGD77
179 files A13232.mgd77 and A99938.mgd77, using the MGD77 tag, try
180 gmt x2sys_cross A13232.mgd77 A99938.mgd77 -Qe -TMGD77 > crossovers.d
182
184 Wessel, P. (2010), Tools for analyzing intersecting tracks: the x2sys
185 package. Computers and Geosciences, 36, 348-354.
186 Wessel, P. (1989), XOVER: A cross-over error detector for track data,
188 Computers and Geosciences, 15(3), 333-346.
189
191 gmt, x2sys_binlist, x2sys_init, x2sys_datalist, x2sys_get, x2sys_list,
192 x2sys_put, x2sys_report, x2sys_solve, x_over
193
195 2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
1965.4.5 Feb 24, 2019 X2SYS_CROSS(1)