NAME
splitxyz - filter to divide (x,y,z[,distance,heading]) data into
(x,y,z) track segments.
SYNOPSIS
splitxyz [ xyz[dh]file ] -Ccourse_change -Dminimum_distance [ -Aaz-
imuth/tolerance ] [ -Fxy_filter/z_filter ] [ -Ggap_distance ] [
-H[nrec] ] [ -M ] [ -Nnamestem ] [ -S ] [ -V ] [ -Z ] [ -: ] [
-bi[s][n] ] [ -bo[s][n] ] [ -f[i|o]colinfo ]
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. 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.
-D Do not write a segment out unless it is at least minimum_dis-
tance units long.
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].
-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 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].
-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 .gmtdefaults4 file. If used, GMT
default is 1 header record. Use -Hi if only input data should
have header records [Default will write out header records if
the input data have them]. 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 >
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 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
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
double]. Append n for the number of columns in the binary
file(s).
-f Special formatting of input and output columns (time or geo-
graphical data) Specify i(nput) or o(utput) [Default is both
input and output]. Give one or more columns (or column ranges)
separated by commas. Append T (Absolute calendar time), t (time
relative to chosen TIME_EPOCH), x (longitude), y (latitude), g
(geographic coordinate), or f (floating point) to each column or
column range item.
EXAMPLES
Suppose you want to make a wiggle plot of magnetic anomalies on seg-
ments 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
-D100 -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 -D100 -: -M -bi3
SEE ALSO
gmt(l), gmtlist(l), pswiggle(l)
GMT4.0 1 Oct 2004 SPLITXYZ(l)
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