gmtsplit(cmd0::String="", arg1=nothing; kwargs...)

keywords: GMT, Julia, break lines

Split xyz[dh] data tables into individual segments


gmtsplit reads a series of (x,y[,z]) records [or optionally (x,y[,z],d,h); see |-S| option] from standard input [or xy[z][dh]file] and splits this into separate lists of (x,y[,z]) series, such that each series has a nearly constant azimuth through the x,y plane. There are options to choose only those series which have a certain orientation, to set a minimum length for series, and to high- or low-pass filter the z values and/or the x,y values. gmtsplit is a useful filter between data extraction and wiggle plotting, and can also be used to divide a large x,y[,z] dataset into segments.

Required Arguments

  • table
    Data from file or a in-memory array with 2, 3, or 5 columns holding (x,y,[z[,d,h]]) data values. To use (x,y,z,d,h) input, sorted so that d is non-decreasing, specify the dist_head option; default expects (x,y,z) only.

Optional Arguments

  • A or azim_tol : – azim_tol=(azimuth,tolerance)
    Write out only those segments which are within ±tolerance degrees of azimuth in heading,measured clockwise from North, [0 - 360]. [Default writes all acceptable segments, regardless of orientation].

  • C or course_change : – course_change=ang
    Terminate a segment when a course change exceeding ang degrees of heading is detected [ignore course changes].

  • D or min_dist or min_distance : – min_dist=distance Do not write a segment out unless it is at least distance units long [0].

  • F or filter : – filter=(xy_filter,z_filter) Filter the z values and/or the x,y values, assuming these are functions of d coordinate. xy_filter and z_filter are filter widths in distance units. If a filter width is zero, the filtering is not performed. The absolute value of the width is the full width of a cosine-arch low-pass filter. If the width is positive, the data are low-pass filtered; if negative, the data are high-pass filtered by subtracting the low-pass value from the observed value. If z_filter is non-zero, the entire series of input z values is filtered before any segmentation is performed, so that the only edge effects in the filtering will happen at the beginning and end of the complete data stream. If xy_filter is non-zero, the data is first divided into segments and then the x,y values of each segment are filtered separately. This may introduce edge effects at the ends of each segment, but prevents a low-pass x,y filter from rounding off the corners of track segments. [Default = no filtering].

N or multifile or multi : – multifile=true | multifile="template"
Write each segment to a separate output file. Default returns data in a GMTdataset. Optionally append a format template for the individual file names; this template must contain a C format specifier that can format an integer argument (the running segment number across all tables); this is usually %d but could be %08d which gives leading zeros, etc. [Default is gmtsplit_segment_%d.{txt\|bin}, depending on binary_out]. Alternatively, give a template with two C format specifiers and we will supply the table number and the segment number within the table to build the file name.

  • Q or fields : – fields=:flags
    Specify your desired output using any combination of xyzdh, in any order. Do not space between the letters. Use lower case. Default is fields=xyzdh (fields=xydh if only 2 input columns).

  • S or dist_head : – dist_head=true
    Both d and h are supplied. In this case, input contains x,y,z,d,h. [Default expects (x,y,z) input, and d,h are computed from delta x, delta y. Use colinfo=:g to indicate map data; then x,y are assumed to be in degrees of longitude, latitude, distances are considered to be in kilometers, and angles are actually azimuths. Otherwise, distances are Cartesian in same units as x,y and angles are counter-clockwise from horizontal].

  • V or verbose : – verbose=true | verbose=level
    Select verbosity level. More at verbose

  • bi or binary_in : – binary_in=??
    Select native binary format for primary table input. More at

  • bo or binary_out : – binary_out=??
    Select native binary format for table output. More at

  • di or nodata_in : – nodata_in=??
    Substitute specific values with NaN. More at

  • e or pattern : – pattern=??
    Only accept ASCII data records that contain the specified pattern. More at

  • f or colinfo : – colinfo=??
    Specify the data types of input and/or output columns (time or geographical data). More at

.. |Add_-g| replace:: Do not let a segment have a gap exceeding gap; instead, split it into two segments. [Default ignores gaps].

  • h or header : – header=??
    Specify that input and/or output file(s) have n header records. More at

  • i or incol or incols : – incol=col_num | incol="opts"
    Select input columns and transformations (0 is first column, t is trailing text, append word to read one word only). More at incol

  • q or inrows : – inrows=??
    Select specific data rows to be read and/or written. More at

  • s or skiprows or skip_NaN : – skip_NaN=true | skip_NaN="<cols[+a][+r]>"
    Suppress output of data records whose z-value(s) equal NaN. More at

  • yx : – yx=true
    Swap 1st and 2nd column on input and/or output. More at

Distance Calculations

The type of input data is dictated by the colinfo option. If colinfo=:g is given then x,y are in degrees of longitude, latitude, distances are in kilometers, and angles are azimuths. Otherwise, distances are Cartesian in same units as x,y and angles are counter-clockwise from horizontal.


Suppose you want to make a wiggle plot of magnetic anomalies on segments oriented approximately east-west from a NCEI-supplied cruise called JA020015 in the region region=(300,315,12,20). You want to use a 100 km low-pass filter to smooth the tracks and a 500km high-pass filter to detrend the magnetic anomalies. Try this:

D = gmt("mgd77list JA020015 -R300/315/12/20 -Flon,lat,mag,dist,azim");
    D = split(D, azim_tol=(90,15), filter=(100,-500), min_dist=100, disthead=true, colinfo=:g);
    wiggle(region=(300,315,12,20), proj=:Merc, scale=1.5, title="JA020015", track=1,
           pen=0.75, fill=:gray, ampscale=200, show=true)

MGD-77 users: For this application we recommend that you extract dist,azim from mgd77list <supplements/mgd77/mgd77list> rather than have gmtsplit compute them separately.

Suppose you have been given a binary, double-precision file containing lat, lon, gravity values from a survey, and you want to split it into profiles named survey_###.txt (when gap exceeds 100 km). Try this:

gmtsplit("survey.bin", multi="survey_%03d.txt", gap="d100k", min_dist=100,
             yx=true, colinfo=:g, binary_in="3d")

See Also

filter1d, wiggle