NAME¶
gmtstitch - Join line segments whose end points match within tolerance
SYNOPSIS¶
gmtstitch [
infiles ] [
-C[
closed] ] [
-D[
template] ] [
-H[
i][
nrec] ] [
-L[
linkfile] ] [
-Q[
template] ] [
-Tcutoff[
m|
c|
e|
E|
k|
K][/
nn_dist] ] [
-V ] [
-:[
i|
o] ] [
-b[
i|
o][
s|
S|
d|
D[
ncol]|
c[
var1/...]]
] [
-bo[
s|
S|
d|
D[
ncol]|
c[
var1
/...]] ] [
-m[
i|
o][
flag] ]
DESCRIPTION¶
gmtstitch reads one or more data files (which may be multisegment files;
see
-m) 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. It 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.
- file(s)
- One of more data files. If none are supplied then we read standard
input.
OPTIONS¶
- -C
- Write all the closed polygons to closed [gmtstitch_closed.d] and
all other segments as they are to stdout. No stitching takes place. Use
-Tcutoff to set a minimum separation [0], and if
cutoff is > 0 then we also close the polygons on output.
- -D
- For multiple segment data, dump each segment to a separate output file
[Default writes a multiple segment file to stdout]. 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 %8.8d 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 gmtstitch_segment_%d.d]. 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 stitched pieces came from.
- -H
- Input file(s) has header record(s). If used, the default number of header
records is N_HEADER_RECS. Use -Hi if only input data should
have header records [Default will write out header records if the input
data have them]. Blank lines and lines starting with # are always
skipped.
- -L
- Writes the link information to the specified file [links.d]. 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
- 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
gmtstitch_list.d].
- -T
- Specifies the separation tolerance in the data coordinate units [0].
Append m or c for minutes or seconds, or e or
k for meters or km (implies -fg using use flat Earth
approximation. Use E or K for exact geodesic distances;
however. if the current ELLIPSOID is Sphere then spherical great circle
distances are used. If two lines has endpoints 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 is assumed to
be in the same units as cutoff.
- -V
- Selects verbose mode, which will send progress reports to stderr [Default
runs "silently"].
- -:
- Toggles between (longitude,latitude) and (latitude,longitude) input and/or
output. [Default is (longitude,latitude)]. Append i to select input
only or o to select output only. [Default affects both].
- -bi
- Selects binary input. Append s for single precision [Default is
d (double)]. Uppercase S or D will force
byte-swapping. Optionally, append ncol, the number of columns in
your binary input file if it exceeds the columns needed by the program. Or
append c if the input file is netCDF. Optionally, append
var1 /var2/... to specify the variables
to be read. [Default is 2 input columns].
- -bo
- Selects binary output. Append s for single precision [Default is
d (double)]. Uppercase S or D will force
byte-swapping. Optionally, append ncol, the number of desired
columns in your binary output file. [Default is same as input].
- -f
- Special formatting of input and/or output columns (time or geographical
data). Specify i or o to make this apply only to input or
output [Default applies to both]. Give one or more columns (or column
ranges) separated by commas. Append T (absolute calendar time),
t (relative time in chosen TIME_UNIT since
TIME_EPOCH), x (longitude), y (latitude), or f
(floating point) to each column or column range item. Shorthand
-f[i|o]g means
-f[i|o]0x,1y (geographic
coordinates).
- -m
- Multiple segment file(s). Segments are separated by a special record. For
ASCII files the first character must be flag [Default is '>'].
For binary files all fields must be NaN and -b must set the number
of output columns explicitly. By default the -m setting applies to
both input and output. Use -mi and -mo to give separate
settings to input and output.
The ASCII output formats of numerical data are controlled by parameters in your
.gmtdefaults4 file. Longitude and latitude are formatted according to
OUTPUT_DEGREE_FORMAT, whereas other values are formatted according to
D_FORMAT. Be aware that the format in effect can lead to loss of
precision in the 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
D_FORMAT setting.
EXAMPLES¶
To combine the digitized multisegment lines segment_*.d (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
gmtstitch segment_*.d
-Tf 0.1
-m > new_segments.d
To combine the digitized segments in the multisegment file my_lines.d (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
gmtstitch my_lines.d
-Tf 0.15k
-m -D
Map_segment_%4.4d.dat
BUGS¶
The line connection does not work if a line only has a single point. However,
gmtstitch will correctly add the point to the nearest segment. Running
gmtstitch again on the new set of lines will eventually connect all close
lines.
SEE ALSO¶
GMT(1),
mapproject(1)