NAME

       gmtconnect - Connect individual lines whose end points match within tolerance

SYNOPSIS

       gmtconnect [ table ] [  -C[closed] ] [  -D[template] ] [  -L[linkfile] ] [  -Q[template] ]
       [  -T[cutoff[unit][/nn_dist]] ] [  -V[level] ] [ -bbinary ] [ -dnodata ] [  -eregexp  ]  [
       -fflags ] [ -ggaps ] [ -hheaders ] [ -iflags ] [ -oflags ] [ -:[i|o] ]

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

DESCRIPTION

       gmtconnect  reads  standard  input  or  one  or more data files, which may be multisegment
       files, 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 tolerance
       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 -L to get a list of all separation distances and
       analyze them to determine a suitable cutoff.

REQUIRED ARGUMENTS

       None.

OPTIONAL ARGUMENTS

       table  One or more ASCII (or binary, see -bi[ncols][type]) data table  file(s)  holding  a
              number of data columns. If no tables are given then we read from standard input.

       -C[closed]
              Write  all  the  closed  polygons  to  closed [gmtconnect_closed.txt] and all other
              segments as they are to stdout. No connection takes place. Use -Tcutoff  to  set  a
              minimum  separation  [0],  and  if  cutoff is > 0 then we also explicitly close the
              polygons on output.

       -D[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 which
              gives 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 gmtconnect_segment_%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[linkfile]
              Writes  the  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 closest segment, whether it is the beginning
              (B) or end (E) point that is closest, and the  distance  between  those  points  in
              units determined by -T.

       -Q[template]
              Used  with  -D  to  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[cutoff[unit][/nn_dist]]
              Specifies the separation  tolerance  in  the  data  coordinate  units  [0];  append
              distance  unit  (see  UNITS). If two lines has end-points that are closer than this
              cutoff they will be joined. Optionally, append /nn_dist which adds the  requirement
              that a link will only be made if the second closest connection exceeds the nn_dist.
              The latter distance must be given in the same units  as  cutoff.   However,  if  no
              arguments are given then we close every polygon regardless of the gap between first
              and last point.

       -V[level] (more ...)
              Select verbosity level [c].

       -bi[ncols][t] (more ...)
              Select native binary input. [Default is 2 input columns].

       -bo[ncols][type] (more ...)
              Select native binary output. [Default is same as input].

       -d[i|o]nodata (more ...)
              Replace input columns that equal nodata with NaN and do the reverse on output.

       -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
              Only accept data records that match the given pattern.

       -f[i|o]colinfo (more ...)
              Specify data types of input and/or output columns.

       -g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (more ...)
              Determine data gaps and line breaks.

       -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
              Skip or produce header record(s).

       -icols[+l][+sscale][+ooffset][,...] (more ...)
              Select input columns and transformations (0 is first column).

       -ocols[,...] (more ...)
              Select output columns (0 is first column).

       -:[i|o] (more ...)
              Swap 1st and 2nd column on input and/or output.

       -^ or just -
              Print a short message about the syntax of the command, then exits (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 exits.

       -? or no arguments
              Print a complete usage (help) message, including the explanation  of  all  options,
              then exits.

UNITS

       For  map  distance  unit,  append  unit  d for arc degree, m for arc minute, and s for arc
       second, or e for meter [Default], 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. Prepend - to a distance (or the unit is no  distance  is
       given)  to  perform  "Flat Earth" calculations (quicker but less accurate) or prepend + to
       perform exact geodesic calculations (slower but more accurate).

ASCII FORMAT PRECISION

       The ASCII output formats of numerical data are controlled by parameters in  your  gmt.conf
       file.  Longitude  and latitude are formatted according to FORMAT_GEO_OUT, absolute time is
       under the control of FORMAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating  point
       values are formatted according to FORMAT_FLOAT_OUT. Be aware that the format in effect can
       lead to loss of precision in ASCII output, which can lead to various problems  downstream.
       If  you find the output is not written with enough precision, consider switching to binary
       output (-bo if available) or specify more decimals using the FORMAT_FLOAT_OUT setting.

EXAMPLES

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

              gmt connect segment_*.txt -Tf0.1 > new_segments.txt

       To combine the digitized segments in the multisegment file my_lines.txt (whose coordinates
       are in lon,lat) into as few complete lines as possible, assuming the end points slop could
       be   up   to   150   m,   and  write  the  complete  segments  to  separate  files  called
       Map_segment_0001.dat, Map_segment_0002.dat, etc., run

              gmt connect my_lines.txt -T150e -DMap_segment_%04d.dat

BUGS

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

SEE ALSO

       gmt, gmt.conf, gmtsimplify, gmtspatial, mapproject

COPYRIGHT

       2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe