1X2SYS_CROSS(1)               Generic Mapping Tools              X2SYS_CROSS(1)
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NAME

6       x2sys_cross - Find and compute crossover errors
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SYNOPSIS

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/...]] ]
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DESCRIPTION

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.
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23       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).
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36       -T     Specify  the  x2sys TAG which tracks the attributes of this data
37              type.
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OPTIONS

40       No space between the option flag and the associated arguments.
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42       -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.
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48       -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
59              CYLINDRICAL PROJECTIONS:
60
61              -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)
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77              CONIC PROJECTIONS:
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79              -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
84              AZIMUTHAL PROJECTIONS:
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86              -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
94              MISCELLANEOUS PROJECTIONS:
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96              -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
105              NON-GEOGRAPHICAL PROJECTIONS:
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107              -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
111       -K     Only process the pair-combinations found in the  file  combi.lis
112              [Default  process  all possible combinations among the specified
113              files].
114
115       -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
120       -Q     Append  e  for  external COEs only, and i for internal COEs only
121              [Default is all COEs].
122
123       -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
135       -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
143       -V     Selects verbose mode, which will send progress reports to stderr
144              [Default runs "silently"].
145
146       -W     Give the maximum number of data points on  either  side  of  the
147              crossover to use in the spline interpolation [3].
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149       -2     Report  the  values  of  each  track  at  the crossover [Default
150              reports the crossover value and the mean value].
151
152       -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

REMARKS

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.
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SIGN CONVENTION

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

PRECISION AND FORMAT

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

EXAMPLES

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
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192       x2sys_cross c2104.gmt -L -TGMT > c2104.d
193
194       To find the crossover locations with bathymetry between the  two  MGD77
195       files A13232.mgd77 and A99938.mgd77, using the MGD77 tag, try
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197       x2sys_cross A13232.mgd77 A99938.mgd77 -Qe -TMGD77 > crossovers.d
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REFERENCES

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

SEE ALSO

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)
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212GMT 4.5.6                         10 Mar 2011                   X2SYS_CROSS(1)
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