gmtconnect
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] ]
[ -b<binary> ]
[ -d<nodata> ]
[ -f<flags> ]
[ -g<gaps> ]
[ -h<headers> ]
[ -i<flags> ]
[ -o<flags> ]
[ -:[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.
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.
- -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 (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 use just -).
- -+ 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
options, then exits.
- --version
- Print GMT version and exit.
- --show-datadir
- Print full path to GMT share directory and exit.
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).
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.