splitxyz - filter to divide (x,y,z[,distance,heading]) data into
(x,y,z) track segments.
splitxyz [ xyz[dh]file ] -Ccourse_change [ -Aazimuth/tolerance ] [
-Dminimum_distance ] [ -Fxy_filter/z_filter ] [ -Ggap_distance ] [
-H[nrec] ] [ -M ] [ -Nnamestem ] [ -S ] [ -V ] [ -Z ] [ -: ] [
-bi[s][n] ] [ -bo[s] ]
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. The output is always in
the ASCII format; input may be ASCII or binary (see -b).
3 (but see -Z) [or 5] column ASCII file [or binary, see -b]
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 file is specified, splitxyz
will read from standard input.
-C Terminate a segment when a course change exceeding course_change
degrees of heading is detected.
-A 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
-D Do not write a segment out unless it is at least minimum_distance
units long. [Default = 100 distance units].
-F 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
filtering 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 performed,
so that the only edge effects in the filtering will happen 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].
-G Do not let a segment have a gap exceeding gap_distance; instead,
split it into two segments. [Default = 10 distance units].
-H Input file(s) has Header record(s). Number of header records can
be changed by editing your .gmtdefaults file. If used, GMT
default is 1 header record. Not used with binary data.
-M Use Map units. Then x,y are in degrees of longitude, latitude,
and distances in kilometers. [Default: distances are cartesian
in same units as x,y].
-N Create Named output files, writing each segment to a separate
file in the working directory named namestem.profile#, where #
increases consecutively from 1. [Default writes entire output to
stdout, separating segments by sub-headings that start with >
-S d and h is 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, according to -M option]
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
-Z Data have x,y only (no z-column).
-: Toggles between (longitude,latitude) and (latitude,longitude)
input/output. [Default is (longitude,latitude)].
-bi Selects binary input. Append s for single precision [Default is
double]. Append n for the number of columns in the binary
file(s). [Default is 2, 3, or 5 input columns as set by -S, -Z].
-bo Selects binary output. Append s for single precision [Default is
Suppose you want to make a wiggle plot of magnetic anomalies on
segments oriented approximately east-west from a cruise called cag71
in the region -R300/315/12/20. You want to use a 100km low-pass
filter to smooth the tracks and a 500km high-pass filter to detrend
the magnetic anomalies. Try this:
gmtlist cag71 -R300/315/12/20 -Fxyzdh | splitxyz -A90/15 -F100/-500 -M
-S -V | pswiggle -R300/315/12/20 -Jm0.6 -Ba5f1:.cag71: -T1 -W3 -G200
-Z200 > cag71_wiggles.ps
MGD-77 users: For this application we recommend that you extract d, h
from gmtlist rather than have splitxyz compute them separately.
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.profile# (when gap exceeds 100 km). Try this:
splitxyz survey.bin -Nsurvey -V -G100 -: -M -bi3
gmt, gmtlist, pswiggle
Man(1) output converted with