# x2sys_list¶

Extract subset from crossover data base

## Synopsis¶

gmt x2sys_list -Ccolumn -TTAG [ coedbase.txt ] [ -Aasymm_max ] [ -E ] [ -Fflags ] [ -I[list] ] [ -L[corrtable] ] [ -Nnx_min[+p] ] [ -Qe|i ] [ -Rregion ] [ -Strack[+b] ] [ -V[level] ] [ -W[list] ] [ -bobinary ] [ --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 stdin) and extract a subset of the crossovers based on the other arguments. The output may be ASCII or binary.

## Required Arguments¶

-Ccolumn
Specify which data column you want to process. Crossovers related to this column name must be present in the crossover data base.
-TTAG
Specify the x2sys TAG which identifies the attributes of this data type.

## Optional Arguments¶

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.
-Aasymm_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 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].
-Fflags
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 dateTclock 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[corrtable]
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.
-Nnx_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].
-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 [±]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). Set geographic regions by specifying ISO country codes from the Digital Chart of the World using -Rcode1,code2,…[+r|R[incs]] instead: Append one or more comma-separated countries using the 2-character ISO 3166-1 alpha-2 convention. To select a state of a country (if available), append .state, e.g, US.TX for Texas. To specify a whole continent, prepend = to any of the continent codes AF (Africa), AN (Antarctica), AS (Asia), EU (Europe), OC (Oceania), NA (North America), or SA (South America). Use +r to modify the bounding box coordinates from the polygon(s): Append inc, xinc/yinc, or winc/einc/sinc/ninc to adjust the region to be a multiple of these steps [no adjustment]. Alternatively, use +R to extend the region outward by adding these increments instead, or +e which is like +r but it ensures that the bounding box extends by at least 0.25 times the increment [no extension]. 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 and registration, if applicable) are copied from the grid. Appending +uunit expects projected (Cartesian) 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 bases the statistics on those COE that fall inside the specified domain.
-Strack[+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] (more …)
Select verbosity level [w].
-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[ncols][type] (more …)
Select native binary 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