1X2SYS_CROSS(1) Generic Mapping Tools X2SYS_CROSS(1)
2
6 x2sys_cross - Find and compute crossover errors
7
9 x2sys_cross track(s) -TTAG [ -Il|a|c ] [ -Jparameters ] [ -Kcombi.lis ]
10 [ -L ] [ -Qe|i ] [ -Sl|u|hspeed ] [ -V ] [ -Wsize ] [ -2 ] [
11 -bo[s|S|d|D[ncol]|c[var1/...]] ]
12
14 x2sys_cross is used to determine all intersections between ("external
15 cross-overs") or within ("internal cross-overs") tracks (Cartesian or
16 geographic), and report the time, position, distance along track, head‐
17 ing and speed along each track segment, and the crossover error (COE)
18 and mean values for all observables. The names of the tracks are
19 passed on the command line. By default, x2sys_cross will look for both
20 external and internal COEs. As an option, you may choose to project
21 all data using one of the map-projections prior to calculating the COE.
22 tracks Can be one or more ASCII, native binary, or COARDS netCDF 1-D
24 data files. To supply the data files via a text file with a
25 list of tracks (one per record), specify the name of the track
26 list after a leading equal-sign (e.g., =tracks.lis). If the
27 names are missing their file extension we will append the suffix
28 specified for this TAG. Track files will be searched for first
29 in the current directory and second in all directories listed in
30 $X2SYS_HOME/TAG/TAG_paths.txt (if it exists). [If $X2SYS_HOME is
31 not set it will default to $GMT_SHAREDIR/x2sys]. (Note: MGD77
32 files will also be looked for via MGD77_HOME/mgd77_paths.txt and
33 *.gmt files will be searched for via $GMT_SHAREDIR/mgg/gmt‐
34 file_paths).
35 -T Specify the x2sys TAG which tracks the attributes of this data
37 type.
38
40 No space between the option flag and the associated arguments.
41 -I Sets the interpolation mode for estimating values at the cross‐
43 over. Choose among:
44 l Linear interpolation [Default].
45 a Akima spline interpolation.
46 c Cubic spline interpolation.
47 -J Selects the map projection. Scale is UNIT/degree, 1:xxxxx, or
49 width in UNIT (upper case modifier). UNIT is cm, inch, or m,
50 depending on the MEASURE_UNIT setting in .gmtdefaults4, but this
51 can be overridden on the command line by appending c, i, or m to
52 the scale/width value. When central meridian is optional,
53 default is center of longitude range on -R option. Default
54 standard parallel is the equator. For map height, max dimen‐
55 sion, or min dimension, append h, +, or - to the width, respec‐
56 tively.
57 More details can be found in the psbasemap man pages.
58 CYLINDRICAL PROJECTIONS:
60 -Jclon0/lat0/scale (Cassini)
62 -Jcyl_stere/[lon0/[lat0/]]scale (Cylindrical Stereographic)
63 -Jj[lon0/]scale (Miller)
64 -Jm[lon0/[lat0/]]scale (Mercator)
65 -Jmlon0/lat0/scale (Mercator - Give meridian and standard paral‐
66 lel)
67 -Jo[a]lon0/lat0/azimuth/scale (Oblique Mercator - point and
68 azimuth)
69 -Jo[b]lon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
70 -Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point and
71 pole)
72 -Jq[lon0/[lat0/]]scale (Cylindrical Equidistant)
73 -Jtlon0/[lat0/]scale (TM - Transverse Mercator)
74 -Juzone/scale (UTM - Universal Transverse Mercator)
75 -Jy[lon0/[lat0/]]scale (Cylindrical Equal-Area)
76 CONIC PROJECTIONS:
78 -Jblon0/lat0/lat1/lat2/scale (Albers)
80 -Jdlon0/lat0/lat1/lat2/scale (Conic Equidistant)
81 -Jllon0/lat0/lat1/lat2/scale (Lambert Conic Conformal)
82 -Jpoly/[lon0/[lat0/]]scale ((American) Polyconic)
83 AZIMUTHAL PROJECTIONS:
85 -Jalon0/lat0[/horizon]/scale (Lambert Azimuthal Equal-Area)
87 -Jelon0/lat0[/horizon]/scale (Azimuthal Equidistant)
88 -Jflon0/lat0[/horizon]/scale (Gnomonic)
89 -Jglon0/lat0[/horizon]/scale (Orthographic)
90 -Jglon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale
91 (General Perspective).
92 -Jslon0/lat0[/horizon]/scale (General Stereographic)
93 MISCELLANEOUS PROJECTIONS:
95 -Jh[lon0/]scale (Hammer)
97 -Ji[lon0/]scale (Sinusoidal)
98 -Jkf[lon0/]scale (Eckert IV)
99 -Jk[s][lon0/]scale (Eckert VI)
100 -Jn[lon0/]scale (Robinson)
101 -Jr[lon0/]scale (Winkel Tripel)
102 -Jv[lon0/]scale (Van der Grinten)
103 -Jw[lon0/]scale (Mollweide)
104 NON-GEOGRAPHICAL PROJECTIONS:
106 -Jp[a]scale[/origin][r|z] (Polar coordinates (theta,r))
108 -Jxx-scale[d|l|ppow|t|T][/y-scale[d|l|ppow|t|T]] (Linear, log,
109 and power scaling)
110 -K Only process the pair-combinations found in the file combi.lis
112 [Default process all possible combinations among the specified
113 files].
114 -L Output results using the old XOVER format [Default is x2sys for‐
116 mat]. This option should only be used with *.gmt-formatted
117 MGD77 files. See the GMT mgg supplement for file description;
118 see Wessel [1989] for details on the XOVER format.
119 -Q Append e for external COEs only, and i for internal COEs only
121 [Default is all COEs].
122 -R west, east, south, and north specify the Region of interest, and
124 you may specify them in decimal degrees or in
125 [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left and
126 upper right map coordinates are given instead of w/e/s/n. The
127 two shorthands -Rg and -Rd stand for global domain (0/360 and
128 -180/+180 in longitude respectively, with -90/+90 in latitude).
129 Alternatively, specify the name of an existing grid file and the
130 -R settings (and grid spacing, if applicable) are copied from
131 the grid. For Cartesian data just give xmin/xmax/ymin/ymax.
132 This option limits the COEs to those that fall inside the speci‐
133 fied domain.
134 -S Defines window of track speeds. If speeds are outside this win‐
136 dow we do not calculate a COE. Specify
137 -Sl sets lower speed [Default is 0].
138 -Su sets upper speed [Default is Infinity].
139 -Sh does not limit the speed but sets a lower speed below
140 which headings will not be computed (i.e., set to NaN) [Default
141 calculates headings regardless of speed].
142 -V Selects verbose mode, which will send progress reports to stderr
144 [Default runs "silently"].
145 -W Give the maximum number of data points on either side of the
147 crossover to use in the spline interpolation [3].
148 -2 Report the values of each track at the crossover [Default
150 reports the crossover value and the mean value].
151 -bo Selects binary output. Append s for single precision [Default
153 is d (double)]. Uppercase S or D will force byte-swapping.
154 Optionally, append ncol, the number of desired columns in your
155 binary output file.
156
158 The COEs found are printed out to standard output in ASCII format
159 (unless -bo is set). When ASCII is chosen, the output format depends
160 on whether or not old-style XOVER output (-L) has been selected [See
161 the x_over man page for more details]. If ASCII, then the first record
162 contains the name of the tag used, the second records specifies the
163 exact command line used for this run, and the third record contains the
164 names of each column. For each track pair, there will be a multiseg‐
165 ment header record containing the two file names and their
166 start/stop/dist information (start/stop is absolute time or NaN if
167 unavailable while dist is the total track length), whereas subsequent
168 records have the data for each COE encountered. The fields written out
169 are x, y, time along track #1 and #2, distance along track #1 and #2,
170 heading along track #1 and #2, velocity along track #1 and #2, and then
171 pairs of columns for each selected observable. These are either pairs
172 of (COE, average value) for each data type (or track-values #1 and #2;
173 see -2). It is recommended that the Akima spline is used instead of
174 the natural cubic spline, since it is less sensitive to outliers that
175 tend to introduce wild oscillations in the interpolation.
176
178 If track_a and track_b are passed on the command line, then the COE
179 value is Value (track_a) - Value (track_b).
180
182 The output format of individual columns are controlled by D_FORMAT
183 except for geographic coordinates (OUTPUT_DEGREE_FORMAT) and absolute
184 calendar time (OUTPUT_DATE_FORMAT, OUTPUT_CLOCK_FORMAT). Make sure
185 these are set to give you enough significant digits to achieve the
186 desired precision.
187
189 To compute all internal crossovers in the gmt-formatted file c2104.gmt,
190 and output in the old XOVER format, using the tag GMT, try
191 x2sys_cross c2104.gmt -L -TGMT > c2104.d
193 To find the crossover locations with bathymetry between the two MGD77
195 files A13232.mgd77 and A99938.mgd77, using the MGD77 tag, try
196 x2sys_cross A13232.mgd77 A99938.mgd77 -Qe -TMGD77 > crossovers.d
198
200 Wessel, P. (2010), Tools for analyzing intersecting tracks: the x2sys
201 package. IT(Computers and Geosciences), BD(36), 348-354.
202 Wessel, P. (1989), XOVER: A cross-over error detector for track data,
203 Computers and Geosciences, 15(3), 333-346.
204
206 GMT(1), x2sys_binlist(1), x2sys_init(1), x2sys_datalist(1),
207 x2sys_get(1), x2sys_list(1), x2sys_put(1), x2sys_report(1),
208 x2sys_solve(1), x_over(1)
209GMT 4.5.6 10 Mar 2011 X2SYS_CROSS(1)