1GMTCONNECT(1) GMT GMTCONNECT(1)
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6 gmtconnect - Connect individual lines whose end points match within
7 tolerance
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10 gmtconnect [ table ] [ -C[closed] ] [ -D[template] ] [ -L[linkfile]
11 ] [ -Q[template] ] [ -T[cutoff[unit][/nn_dist]] ] [ -V[level] ] [
12 -bbinary ] [ -dnodata ] [ -eregexp ] [ -fflags ] [ -ggaps ] [ -hheaders
13 ] [ -iflags ] [ -oflags ] [ -:[i|o] ]
14 Note: No space is allowed between the option flag and the associated
16 arguments.
17
19 gmtconnect reads standard input or one or more data files, which may be
20 multisegment files, and examines the coordinates of the end points of
21 all line segments. If a pair of end points are identical or closer to
22 each other than the specified separation tolerance then the two line
23 segments are joined into a single segment. The process repeats until
24 all the remaining endpoints no longer pass the tolerance test; the
25 resulting segments are then written out to standard output or specified
26 output file. If it is not clear what the separation tolerance should be
27 then use -L to get a list of all separation distances and analyze them
28 to determine a suitable cutoff.
29
31 None.
32
34 table One or more ASCII (or binary, see -bi[ncols][type]) data table
35 file(s) holding a number of data columns. If no tables are given
36 then we read from standard input.
37 -C[closed]
39 Write all the closed polygons to closed [gmtconnect_closed.txt]
40 and all other segments as they are to stdout. No connection
41 takes place. Use -Tcutoff to set a minimum separation [0], and
42 if cutoff is > 0 then we also explicitly close the polygons on
43 output.
44 -D[template]
46 For multiple segment data, dump each segment to a separate out‐
47 put file [Default writes a single multiple segment file]. Append
48 a format template for the individual file names; this template
49 must contain a C format specifier that can format an integer
50 argument (the segment number); this is usually %d but could be
51 %08d which gives leading zeros, etc. Optionally, it may also
52 contain the format %c before the integer; this will then be
53 replaced by C (closed) or O (open) to indicate segment type.
54 [Default is gmtconnect_segment_%d.txt]. Note that segment head‐
55 ers will be written in either case. For composite segments, a
56 generic segment header will be written and the segment headers
57 of individual pieces will be written out as comments to make it
58 possible to identify where the connected pieces came from.
59 -L[linkfile]
61 Writes the link information to the specified file [gmtcon‐
62 nect_link.txt]. For each segment we write the original segment
63 id, and for the beginning and end point of the segment we report
64 the id of the closest segment, whether it is the beginning (B)
65 or end (E) point that is closest, and the distance between those
66 points in units determined by -T.
67 -Q[template]
69 Used with -D to a list file with the names of the individual
70 output files. Optionally, append a filename template for the
71 individual file names; this template may contain a C format
72 specifier that can format an character (C or O for closed or
73 open, respectively). [Default is gmtconnect_list.txt].
74 -T[cutoff[unit][/nn_dist]]
76 Specifies the separation tolerance in the data coordinate units
77 [0]; append distance unit (see UNITS). If two lines has
78 end-points that are closer than this cutoff they will be joined.
79 Optionally, append /nn_dist which adds the requirement that a
80 link will only be made if the second closest connection exceeds
81 the nn_dist. The latter distance must be given in the same units
82 as cutoff. However, if no arguments are given then we close
83 every polygon regardless of the gap between first and last
84 point.
85 -V[level] (more ...)
87 Select verbosity level [c].
88 -bi[ncols][t] (more ...)
90 Select native binary input. [Default is 2 input columns].
91 -bo[ncols][type] (more ...)
93 Select native binary output. [Default is same as input].
94 -d[i|o]nodata (more ...)
96 Replace input columns that equal nodata with NaN and do the
97 reverse on output.
98 -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
100 Only accept data records that match the given pattern.
101 -f[i|o]colinfo (more ...)
103 Specify data types of input and/or output columns.
104 -g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (more ...)
106 Determine data gaps and line breaks.
107 -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
109 Skip or produce header record(s).
110 -icols[+l][+sscale][+ooffset][,...] (more ...)
112 Select input columns and transformations (0 is first column).
113 -ocols[,...] (more ...)
115 Select output columns (0 is first column).
116 -:[i|o] (more ...)
118 Swap 1st and 2nd column on input and/or output.
119 -^ or just -
121 Print a short message about the syntax of the command, then
122 exits (NOTE: on Windows just use -).
123 -+ or just +
125 Print an extensive usage (help) message, including the explana‐
126 tion of any module-specific option (but not the GMT common
127 options), then exits.
128 -? or no arguments
130 Print a complete usage (help) message, including the explanation
131 of all options, then exits.
132
134 For map distance unit, append unit d for arc degree, m for arc minute,
135 and s for arc second, or e for meter [Default], f for foot, k for km, M
136 for statute mile, n for nautical mile, and u for US survey foot. By
137 default we compute such distances using a spherical approximation with
138 great circles. Prepend - to a distance (or the unit is no distance is
139 given) to perform "Flat Earth" calculations (quicker but less accurate)
140 or prepend + to perform exact geodesic calculations (slower but more
141 accurate).
142
144 The ASCII output formats of numerical data are controlled by parameters
145 in your gmt.conf file. Longitude and latitude are formatted according
146 to FORMAT_GEO_OUT, absolute time is under the control of FOR‐
147 MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point val‐
148 ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for‐
149 mat in effect can lead to loss of precision in ASCII output, which can
150 lead to various problems downstream. If you find the output is not
151 written with enough precision, consider switching to binary output (-bo
152 if available) or specify more decimals using the FORMAT_FLOAT_OUT set‐
153 ting.
154
156 To combine the digitized segment lines segment_*.txt (whose coordinates
157 are in cm) into as few complete lines as possible, assuming the end
158 points slop could be up to 0.1 mm, run
159 gmt connect segment_*.txt -Tf0.1 > new_segments.txt
161 To combine the digitized segments in the multisegment file my_lines.txt
163 (whose coordinates are in lon,lat) into as few complete lines as possi‐
164 ble, assuming the end points slop could be up to 150 m, and write the
165 complete segments to separate files called Map_segment_0001.dat,
166 Map_segment_0002.dat, etc., run
167 gmt connect my_lines.txt -T150e -DMap_segment_%04d.dat
169
171 The line connection does not work if a line only has a single point.
172 However, gmtconnect will correctly add the point to the nearest seg‐
173 ment. Running gmtconnect again on the new set of lines will eventually
174 connect all close lines.
175
177 gmt, gmt.conf, gmtsimplify, gmtspatial, mapproject
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180 2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
1815.4.5 Feb 24, 2019 GMTCONNECT(1)