gmtconnect(1) GMT gmtconnect(1)
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 out-
put 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 head-
ers 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 [gmtcon-
nect_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 a|)
Select verbosity level [c].
-bi[ncols][t] (more a|)
Select native binary input. [Default is 2 input columns].
-bo[ncols][type] (more a|)
Select native binary output. [Default is same as input].
-d[i|o]nodata (more a|)
Replace input columns that equal nodata with NaN and do the
reverse on output.
-e[~]^<i>apattern^<i>a | -e[~]/regexp/[i] (more a|)
Only accept data records that match the given pattern.
-f[i|o]colinfo (more a|)
Specify data types of input and/or output columns.
-g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (more a|)
Determine data gaps and line breaks.
-h[i|o][n][+c][+d][+rremark][+rtitle] (more a|)
Skip or produce header record(s).
-icols[+l][+sscale][+ooffset][,^<i>a|] (more a|)
Select input columns and transformations (0 is first column).
-ocols[,a|] (more a|)
Select output columns (0 is first column).
-:[i|o] (more a|)
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 explana-
tion 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 aFlat Eartha 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 FOR-
MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point val-
ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for-
mat 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 set-
ting.
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 possi-
ble, 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 seg-
ment. Running gmtconnect again on the new set of lines will eventually
connect all close lines.
SEE ALSO
gmt(1), gmt.conf(5), gmtsimplify(1), gmtspatial(1), mapproject(1)
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 gmtconnect(1)
gmt5 5.4.2 - Generated Wed Jun 28 16:15:27 CDT 2017