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

keywords: GMT, Julia, line connect

Connect individual lines whose end points match within tolerance


Reads a multi-column data set and examines the coordinates of the end points of all line segments. If a pair of end points are identical or closer to each other than the specified separation cutoff then the two line segments are joined into a single segment. The process repeats until all the remaining endpoints no longer pass the tolerance test; the resulting segments are then written out to standard output or specified output file. If it is not clear what the separation tolerance should be then use linkfile to get a list of all separation distances and analyze them to determine a suitable cutoff.

Required Arguments

  • table
    One or more data tables holding a number of data columns.

Optional Arguments

  • C or closed : – closed=true | closed=closed_file
    Write all the already-closed polygons to file closed [gmtconnect_closed.txt] and all open segments to standard output. No connection will take place. Use tolerance=cutoff to set a minimum separation [0], and then any existing polygon whose first and last point are separated by less that cutoff will be considered to be closed. Note that if cutoff is > 0 then we explicitly close all polygons on output.

  • D or dump : – dump=true | dump="template"
    For multiple segment data, dump each segment to a separate output file [Default writes a single multiple segment file]. Append a format template for the individual file names; this template must contain a C format specifier that can format an integer argument (the segment number); this is usually %d but could be %08d for leading zeros, etc. Optionally, it may also contain the format %c before the integer; this will then be replaced by C (closed) or O (open) to indicate segment type. [Default is gmtconnectsegment%d.txt]. Note that segment headers will be written in either case. For composite segments, a generic segment header will be written and the segment headers of individual pieces will be written out as comments to make it possible to identify where the connected pieces came from.

  • L or links or linkfile : – links=true | linkfile="file"
    Writes link information to the specified file gmtconnect_link.txt. For each segment we write the original segment id, and for the beginning and end point of the segment we report the id of the nearest segment, whether it is the beginning (B) or end (E) point that is closest, and the distance between those points in units determined by tolerance.

  • Q or list or listfile : – list=true | listfile="template"
    Used with dump to write a list file with the names of the individual output files. Optionally, append a filename template for the individual file names; this template may contain a C format specifier that can format an character (C or O for closed or open, respectively). [Default is gmtconnect_list.txt].

  • T or tolerance : – tolerance=true | tolerance=cutoff | tolerance="cutoff+sdist"
    Specifies the separation tolerance in the data coordinate units [0]; for geographic data append distance unit (see Units). If two lines have end-points that are closer than cutoff they will be joined. Optionally, append +s dist which adds the extra requirement that a link will only be made if the second closest connection exceeds the dist distance. The latter distance must be given in the same units as cutoff. However, if tolerance is used with no arguments then we close every line segment or polygon regardless of the gap distance between the first and last point in the segment.

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

  • a or aspatial : – aspatial=??
    Control how aspatial data are handled in GMT during input and output. More at

  • 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

  • g or gap : – gap=??
    Examine the spacing between consecutive data points in order to impose breaks in the line. More at

  • 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

  • o or outcol : – outcol=??
    Select specific data columns for primary output, in arbitrary order. More at

  • 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


For map distance unit, append unit d for arc degree, m for arc minute, and s for arc second, or e for meter [Default unless stated otherwise], f for foot, k for km, M for statute mile, n for nautical mile, and u for US survey foot. By default we compute such distances using a spherical approximation with great circles (-jg) using the authalic radius (see PROJ_MEAN_RADIUS). You can use -jf to perform “Flat Earth” calculations (quicker but less accurate) or -je to perform exact geodesic calculations (slower but more accurate; see PROJ_GEODESIC for method used).


To combine the digitized segment lines segment_*.txt (whose Cartesian coordinates are in cm) into as few complete lines as possible, assuming the end points' digitization error could be up to 0.1 mm, run::

D = connect("segment_*.txt", tolerance=0.1)

To combine the digitized segments in the multisegment file mylines.txt (whose coordinates are in lon,lat) into as few complete lines as possible, assuming the end points digitization error could be up to 150 m, and write the complete segments to individual files called Mapsegment0001.txt, Mapsegment_0002.txt, etc., run::

connect("my_lines.txt", tolerance="150e", dump="Map_segment_%04d.txt")


The line connection does not work if a line only has a single point. However, connect will correctly add the point to the nearest segment. Running connect again on the new set of lines will eventually connect all lines that satisfy the criteria given in tolerance.

See Also

gmtsimplify, gmtspatial, mapproject