splitxyz(1) GMT splitxyz(1)
NAME
splitxyz - Split xyz[dh] data tables into individual segments
SYNOPSIS
splitxyz [ table ] [ -Aazimuth/tolerance ] [ -Ccourse_change] [
-Dminimum_distance ] [ -Fxy_filter/z_filter ] [ -Ntemplate ] [
-Qflags ] [ -S ] [ -V[level] ] [ -bbinary ] [ -dnodata ] [ -eregexp ]
[ -fflags ] [ -ggaps ] [ -hheaders ] [ -iflags ] [ -:[i|o] ]
Note: No space is allowed between the option flag and the associated
arguments.
DESCRIPTION
splitxyz reads a series of (x,y[,z]) records [or optionally
(x,y,z,d,h); see -S option] from standard input [or xyz[dh]file] and
splits this into separate lists of (x,y[,z]) series, such that each
series has a nearly constant azimuth through the x,y plane. There are
options to choose only those series which have a certain orientation,
to set a minimum length for series, and to high- or low-pass filter the
z values and/or the x,y values. splitxyz is a useful filter between
data extraction and pswiggle plotting, and can also be used to divide a
large x,y[,z] dataset into segments.
REQUIRED ARGUMENTS
none.
OPTIONAL ARGUMENTS
table One or more ASCII [or binary, see -bi] files with 2, 3, or 5
columns holding (x,y,[z[,d,h]]) data values. To use (x,y,z,d,h)
input, sorted so that d is non-decreasing, specify the -S
option; default expects (x,y,z) only. If no files are specified,
splitxyz will read from standard input.
-Aazimuth/tolerance
Write out only those segments which are within +/- tolerance
degrees of azimuth in heading, measured clockwise from North, [0
- 360]. [Default writes all acceptable segments, regardless of
orientation].
-Ccourse_change
Terminate a segment when a course change exceeding course_change
degrees of heading is detected [ignore course changes].
-Dminimum_distance
Do not write a segment out unless it is at least minimum_dis-
tance units long [0]
-Fxy_filter/z_filter
Filter the z values and/or the x,y values, assuming these are
functions of d coordinate. xy_filter and z_filter are filter
widths in distance units. If a filter width is zero, the filter-
ing is not performed. The absolute value of the width is the
full width of a cosine-arch low-pass filter. If the width is
positive, the data are low-pass filtered; if negative, the data
are high-pass filtered by subtracting the low-pass value from
the observed value. If z_filter is non-zero, the entire series
of input z values is filtered before any segmentation is per-
formed, so that the only edge effects in the filtering will hap-
pen at the beginning and end of the complete data stream. If
xy_filter is non-zero, the data is first divided into segments
and then the x,y values of each segment are filtered separately.
This may introduce edge effects at the ends of each segment, but
prevents a low-pass x,y filter from rounding off the corners of
track segments. [Default = no filtering].
-Ntemplate
Write 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 running seg-
ment number across all tables); this is usually %d but could be
%08d which gives leading zeros, etc. [Default is splitxyz_seg-
ment_%d.{txt|bin}, depending on -bo]. Alternatively, give a tem-
plate with two C format specifiers and we will supply the table
number and the segment number within the table to build the file
name.
-Qflags
Specify your desired output using any combination of xyzdh, in
any order. Do not space between the letters. Use lower case. The
output will be ASCII (or binary, see -bo) columns of values cor-
responding to xyzdh [Default is -Qxyzdh (-Qxydh if only 2 input
columns)].
-S Both d and h are supplied. In this case, input contains
x,y,z,d,h. [Default expects (x,y,z) input, and d,h are computed
from delta x, delta y. Use -fg to indicate map data; then x,y
are assumed to be in degrees of longitude, latitude, distances
are considered to be in kilometers, and angles are actually
azimuths. Otherwise, distances are Cartesian in same units as
x,y and angles are counter-clockwise from horizontal].
-V[level] (more a|)
Select verbosity level [c].
-bi[ncols][t] (more a|)
Select native binary input. [Default is 2, 3, or 5 input columns
as set by -S].
-bo[ncols][type] (more a|)
Select native binary output. [Default is 1-5 output columns as
set by -Q].
-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. Do not let a segment have a
gap exceeding gap; instead, split it into two segments. [Default
ignores gaps].
-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).
-:[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.
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.
DISTANCE CALCULATIONS
The type of input data is dictated by the -f option. If -fg is given
then x,y are in degrees of longitude, latitude, distances are in kilo-
meters, and angles are azimuths. Otherwise, distances are Cartesian in
same units as x,y and angles are counter-clockwise from horizontal.
EXAMPLES
Suppose you want to make a wiggle plot of magnetic anomalies on seg-
ments oriented approximately east-west from a NGDC-supplied cruise
called JA020015 in the region -R300/315/12/20. You want to use a 100 km
low-pass filter to smooth the tracks and a 500km high-pass filter to
detrend the magnetic anomalies. Try this:
gmt mgd77list JA020015 -R300/315/12/20 -Flon,lat,mag,dist,azim | gmt splitxyz -A90/15 -F100/-500 \
-D100 -S -V -fg | gmt pswiggle -R300/315/12/20 -Jm0.6i -Baf -B+tJA020015 -T1 \
-W0.75p -Ggray -Z200 > JA020015_wiggles.ps
MGD-77 users: For this application we recommend that you extract
dist,azim from mgd77list rather than have splitxyz compute them sepa-
rately.
Suppose you have been given a binary, double-precision file containing
lat, lon, gravity values from a survey, and you want to split it into
profiles named survey_###.txt (when gap exceeds 100 km). Try this:
gmt splitxyz survey.bin -Nsurvey_%03d.txt -V -gd100k -D100 -: -fg -bi3d
SEE ALSO
gmt(1), filter1d(1), mgd77list(1), pswiggle(1)
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 splitxyz(1)
gmt5 5.4.2 - Generated Thu Jun 29 16:33:53 CDT 2017