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Manual Reference Pages  -  X2SYS_DATALIST (1)


x2sys_datalist - A generic data-extractor for ASCII or binary files




x2sys_datalist track(s) -TTAG [ -A ] [ -Fname1,name2,... ] [ -H[i][nrec] ] [ -L[corrtable] ] [ -Rwest/east/south/north[r] ] [ -S ] [ -V ] [ -bo[s|S|d|D[ncol]|c[var1/...]] ] [ -m[flag] ]


x2sys_datalist reads one or more files and produces a single ASCII [or binary] table. The files can be of any format, which must be described and passed with the -T option. You may limit the output to a geographic region, and insist that the output from several files be separated by a multiple segment header. Only the named data fields will be output [Default selects all columns].
tracks Can be one or more ASCII, native binary, or COARDS netCDF 1-D data files. To supply the data files via a text file with a list of tracks (one per record), specify the name of the track list after a leading equal-sign (e.g., =tracks.lis). If the names are missing their file extension we will append the suffix specified for this TAG. Track files will be searched for first in the current directory and second in all directories listed in $X2SYS_HOME/TAG/TAG_paths.txt (if it exists). [If $X2SYS_HOME is not set it will default to $GMT_SHAREDIR/x2sys]. (Note: MGD77 files will also be looked for via MGD77_HOME/mgd77_paths.txt and *.gmt files will be searched for via $GMT_SHAREDIR/mgg/gmtfile_paths).
-T Specify the x2sys TAG which tracks the attributes of this data type.


No space between the option flag and the associated arguments.
-A Eliminate COEs by distributing the COE between the two tracks in proportion to track weight. These (dist, adjustment) spline knots files for each track and data column are called track.column.adj and are expected to be in the $X2SYS_HOME/TAG directory. The adjustments are only applied if the corresponding adjust file can be found [No residual adjustments]
-F Give a comma-separated sub-set list of column names defined in the definition file. [Default selects all data columns].
-H Input file(s) has header record(s). If used, the default number of header records is N_HEADER_RECS. Use -Hi if only input data should have header records [Default will write out header records if the input data have them]. Blank lines and lines starting with # are always skipped.
-L Apply optimal corrections to columns where such corrections are available. 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 CORRECTIONS below.
-R west, east, south, and north specify the Region of interest, and you may specify them in decimal degrees or in [+-]dd:mm[][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). Alternatively, specify the name of an existing grid file and the -R settings (and grid spacing, if applicable) are copied from the grid. For Cartesian data just give xmin/xmax/ymin/ymax. This option limits the COEs to those that fall inside the specified domain.
-S Suppress output records where all the data columns are NaN [Default will output all records].
-V Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].
-bo Selects binary output. Append s for single precision [Default is d (double)]. Uppercase S or D will force byte-swapping. Optionally, append ncol, the number of desired columns in your binary output file.
-m Output a multisegment header between data from each track. Note this option does not imply anything about the input file; that information is conveyed via the system tag (-T).


To extract all data from the old-style MGG supplement file c2104.gmt, recognized by the tag GMT:

x2sys_datalist c2104.gmt -T GMT > myfile

To make lon,lat, and depth input for blockmean and surface using all the files listed in the file tracks.lis and define by the tag TRK, but only the data that are inside the specified area, and make output binary, run

x2sys_datalist =tracks.lis -T TRK -F lon,lat,depth -R-40/-30/25/35 -bo >


The correction table is an ASCII file with coefficients and parameters needed to carry out corrections. This table is usually produced by x2sys_solve. Comment records beginning with # are allowed. All correction records are of the form

trackID observation correction

where trackID is the track name, observation is one of the abbreviations for an observed field contained in files under this TAG, and correction consists of one or more white-space-separated terms that will be subtracted from the observation before output. Each term must have this exact syntax:


where terms in brackets are optional (the brackets themselves are not used but regular parentheses must be used exactly as indicated). No spaces are allowed except between terms. The factor is the amplitude of the basis function, while the optional function can be one of sin, cos, or exp. The optional scale and origin can be used to translate the argument (before giving it to the optional function). The argument abbrev is one of the abbreviations for columns known to this TAG. However, it can also be one of the three auxiliary terms dist (for along-track distances), azim for along-track azimuths, and vel (for along-track speed); these are all sensitive to the -C and -N settings used when defining the TAB; furthermore, vel requires time to be present in the data. If origin is given as T it means that we should replace it with the value of abbrev for the very first record in the file (this is usually only done for time). If the first data record entry is NaN we revert origin to zero. Optionally, raise the entire expression to the given power, before multiplying by factor. The following is an example of fictitious corrections to the track ABC, implying the z column should have a linear trend removed, the field obs should be corrected by a strange dependency on latitude, weight needs to have 1 added (hence correction is given as -1), and fuel should be reduced by a linear distance term:

ABC z   7.1     1e-4*((time-T))
ABC obs 0.5*exp(-1e-3(lat))^1.5
ABC weight      -1
ABC fuel 0.02*((dist))


blockmean(1), GMT(1), surface(1), x2sys_init(1), x2sys_datalist(1), x2sys_get(1), x2sys_list(1), x2sys_put(1), x2sys_report(1), x2sys_solve(1)
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GMT 4.5.14 X2SYS_DATALIST (1) 1 Nov 2015

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