NAME
splitxyz - filter to divide (x,y,z[,distance,heading]) data
into (x,y,z) track segments.
SYNOPSIS
splitxyz [ xyz[dh]file ] - Ccourse_change [ -
Aazimuth/tolerance ] [ - Dminimum_distance ] [ -
Fxy_filter/z_filter ] [ -Ggap_distance ] [ -H ] [ -M ] [ -
Nnamestem ] [ -S ] [ -V ] [ -Z ] [ -: ] [ -b[d] ]
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 con-
stant 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).
xyz[dh]file(s)
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.
OPTIONS
-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 orientation].
-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 begin-
ning 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: dis-
tances 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 > marks].
-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)]
-b Selects binary input mode [Default is ASCII]. Append
d to indicate double precision for binary data [Default
is single].
EXAMPLES
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 -bd
SEE ALSO
gmt, gmtlist, pswiggle
REFERENCES
Wessel, P., and W. H. F. Smith, 1995, The Generic Mapping
Tools (GMT) version 3.0 Technical Reference & Cookbook,
SOEST/NOAA.
Wessel, P., and W. H. F. Smith, 1995, New Version of the
Generic Mapping Tools Released, EOS Trans. AGU, 76, p. 329.
Wessel, P., and W. H. F. Smith, 1995, New Version of the
Generic Mapping Tools Released,
http://www.agu.org/eos_elec/95154e.html, Copyright 1995 by
the American Geophysical Union.
Wessel, P., and W. H. F. Smith, 1991, Free Software Helps
Map and Display Data, EOS Trans. AGU, 72, p. 441.