# x2sys_list

Extract subset from crossover data base

## Synopsis

gmt x2sys_list -C column -T TAG [ coedbase.txt ] [ -A asymm_max ] [ -E ] [ -F flags ] [ -I[list] ] [ -L[corrections] ] [ -N nx_min[+p] ] [ -Q e|i ] [ -R region ] [ -S track[+b] ] [ -V[level] ] [ -W[list] ] [ -bo binary ] [ --PAR=value ]

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

## Description

x2sys_list will read the crossover ASCII data base coedbase.txt (or standard input) and extract a subset of the crossovers based on the other arguments. The output may be ASCII or binary.

## Required Arguments

-C column

  Specify which data column you want to process. Crossovers related to this column name must be present in the crossover data base.

-T TAG

  Specify the x2sys TAG which identifies the attributes of this data type.

coedbase.txt

  The name of the input ASCII crossover error data base as produced by x2sys_cross. If not given we read standard input instead.

## Optional Arguments

-A asymm_max

  Specifies maximum asymmetry in the distribution of crossovers relative to the mid point in time (or distance, if not time is available). Asymmetry is computed as (n_right - n_left)/(n_right + n_left), referring the number of crossovers that falls in the left or right half of the range. Symmetric distributions will have values close to zero. If specified, we exclude tracks whose asymmetry exceeds the specify cutoff in absolute value [1, i.e., include all].

-E

  Enhance ASCII output by writing GMT segment headers with names of the two tracks and their total number of cross-overs [no segment headers].

-F flags

  Specify your desired output using any combination of acdhiInNtTvwxyz, in any order. Do not use space between the letters, and note your selection is case-sensitive. The output will be ASCII (or binary, -bo) columns of values. Description of codes: a is the angle (< 90) defined by the crossing tracks, c is crossover value of chosen observation (see -C), d is distance along track, h is heading along track, i is the signed time interval between the visit at the crossover of the two tracks involved, I is same as i but is unsigned, n is the names of the two tracks, N is the id numbers of the two tracks, t is time along track in date T clock format (NaN if not available), T is elapsed time since start of track along track (NaN if not available), v is speed along track, w is the composite weight, x is x-coordinate (or longitude), y is y-coordinate (or latitude), and z is observed value (see -C) along track. If -S is not specified then d,h,n,N,t,T,v results in two output columns each: first for track one and next for track two (in lexical order of track names); otherwise, they refer to the specified track only (except for n,N which then refers to the other track). The sign convention for c,i is track one minus track two (lexically sorted). Time intervals will be returned according to the TIME_UNIT GMT defaults setting. The output order of the columns follows the order they were given in flags with the exception that n, if chosen, will always be placed after all numeric columns (it becomes part of the trailing text).

-I[list]

  Name of ASCII file with a list of track names (one per record) that should be excluded from consideration [Default includes all tracks].

-L[corrections]

  Apply optimal corrections to the chosen observable. Append the correction table to use [Default uses the correction table TAG_corrections.txt which is expected to reside in the $X2SYS_HOME/TAG directory]. For the format of this file, see x2sys_solve.

-N nx_min[+p]

  Suppress all crossovers involving tracks that did not generate at least a total of nx_min crossings with all other tracks. Alternatively, append +p to instead suppress data from pairs that generated less than nx_min crossovers between them [use all pairs].

-Qe|i

  Append e for external crossovers or i for internal crossovers only [Default is all crossovers].

-R west/east/south/north[/zmin/zmax][+r][+u unit]

> Specify the region of interest. For Cartesian data just give xmin/xmax/ymin/ymax. This option bases the statistics on those COE that fall inside the specified domain.

> The region may be specified in one of several ways:

> 1. -R west/east/south/north. This is the standard way to specify geographic regions when using map projections where meridians and parallels are rectilinear. The coordinates may be specified in decimal degrees or in [±]dd:mm[:ss.xxx][W|E|S|N] format.

> 2. -R west/south/east/north+r. This form is useful for map projections that are oblique, making meridians and parallels poor choices for map boundaries. Here, we instead specify the lower left corner and upper right corner geographic coordinates, followed by the modifier +r. This form guarantees a rectangular map even though lines of equal longitude and latitude are not straight lines.

> 3. -Rg or -Rd. These forms can be used to quickly specify the global domain (0/360 for -Rg and -180/+180 for -Rd in longitude, with -90/+90 in latitude).

> 4. -R code1,code2,…[+e|r|R incs]. This indirectly supplies the region by consulting the DCW (Digital Chart of the World) database and derives the bounding regions for one or more countries given by the codes. Simply append one or more comma-separated countries using either the two-character ISO 3166-1 alpha-2 convention (e.g., NO) or the full country name (e.g., Norway). To select a state within a country (if available), append .state (e.g, US.TX), or the full state name (e.g., Texas). To specify a whole continent, spell out the full continent name (e.g., -RAfrica). Finally, append any DCW collection abbreviations or full names for the extent of the collection or named region. All names are case-insensitive. The following modifiers can be appended:

>    > - +r to adjust the region boundaries to be multiples of the steps indicated by inc, xinc/yinc, or winc/einc/sinc/ninc [default is no adjustment]. For example, -R FR+r1 will select the national bounding box of France rounded to nearest integer degree, where inc can be positive to expand the region or negative to shrink the region.

>    > - +R to adjust the region by adding the amounts specified by inc, xinc/yinc, or winc/einc/sinc/ninc [default is no extension], where inc can be positive to expand the region or negative to shrink the region.

>    > - +e to adjust the region boundaries to be multiples of the steps indicated by inc, xinc/yinc, or winc/einc/sinc/ninc, while ensuring that the bounding box is adjusted by at least 0.25 times the increment [default is no adjustment], where inc can be positive to expand the region or negative to shrink the region.

> 5. -R xmin/xmax/ymin/ymax[+u unit] specifies a region in projected units (e.g., UTM meters) where xmin/xmax/ymin/ymax are Cartesian projected coordinates compatible with the chosen projection (-J) and unit is an allowable distance unit [e]; we inversely project to determine the actual rectangular geographic region. For projected regions centered on (0,0) you may use the short-hand -R halfwidth[/halfheight]+u unit, where halfheight defaults to halfwidth if not given. This short-hand requires the +u modifier.

> 6. -R justifylon0/lat0/nx/ny, where justify 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). The two character code justify indicates which point on a rectangular region region the lon0/lat0 coordinates refer to and the grid dimensions nx and ny are used with grid spacings given via -I to create the corresponding region. This method can be used when creating grids. For example, -RCM 25/25/50/50 specifies a 50x50 grid centered on 25,25.

> 7. -R gridfile. This will copy the domain settings found for the grid in specified file. Note that depending on the nature of the calling module, this mechanism will also set grid spacing and possibly the grid registration (see Grid registration: The -r option).

> 8. -Ra[uto] or -Re[xact]. Under modern mode, and for plotting modules only, you can automatically determine the region from the data used. You can either get the exact area using -Re [Default if no -R is given] or a slightly larger area sensibly rounded outwards to the next multiple of increments that depend on the data range using -Ra.

-S track[+b]

  Name of a single track. If given we restrict output to those crossovers involving this track [Default output is crossovers involving any track pair]. Append +b to print info relative to both tracks in the pair.

-V[level]

  Select verbosity level [w]. (See full description) (See cookbook information).

-W[list]

  Name of ASCII file with a list of track names and their relative weights (one track per record) that should be used to calculate the composite crossover weight (output code w above). [Default sets weights to 1].

-bo record[+b|l] (more …)

  Select native binary format for table output.

-^ or just -

  Print a short message about the syntax of the command, then exit (Note: on Windows just use -).

-+ or just +

  Print an extensive usage (help) message, including the explanation of any module-specific option (but not the GMT common options), then exit.

-? or no arguments

  Print a complete usage (help) message, including the explanation of all options, then exit.

--PAR=value

  Temporarily override a GMT default setting; repeatable. See gmt.conf for parameters.

## Input Format

In moving to a more robust data record definition in GMT 6, all text items are now placed after all numerical items. For x2sys_list, this means that whereas the ID1, ID2 track ids used to be written to the first two columns, they are now placed at the end as part of the trailing text.

## Examples

To find all the magnetic crossovers associated with the tag MGD77 from the file COE_data.txt, restricted to occupy a certain region in the south Pacific, and return location, time, and crossover value, try:

    gmt x2sys_list COE_data.txt -V -TMGD77 -R180/240/-60/-30 -Cmag -Fxytz > mag_coe.txt

To find all the faa crossovers globally that involves track 12345678 and output time since start of the year, using a binary double precision format, try:

    gmt x2sys_list COE_data.txt -V -TMGD77 -Cfaa -S12345678 -FTz -bod > faa_coe.b

## References

Wessel, P. (2010), Tools for analyzing intersecting tracks: the x2sys package. Computers and Geosciences, 36, 348-354, https://www.researchgate.net/publication/220164039_Tools_for_analyzing_intersecting_tracks_The_x2sys_package.

Wessel, P. (1989), XOVER: A cross-over error detector for track data, Computers and Geosciences, 15(3), 333-346, https://doi.org/10.1016/0098-3004(89)90044-7.

## See Also

x2sys_binlist, x2sys_cross, x2sys_datalist, x2sys_get, x2sys_init, x2sys_put, x2sys_report, x2sys_solve