SYNOPSIS

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][n] ]

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.

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 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 > 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)]. Applies to geographic coordinates only.

-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].

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 -bi3