1SPLITXYZ(1) Generic Mapping Tools SPLITXYZ(1)
2
6 splitxyz - filter to divide (x,y,z[,distance,heading]) data into
7 (x,y,z) track segments.
8
10 splitxyz [ xyz[dh]file ] -Ccourse_change [ -Aazimuth/tolerance ] [
11 -Dminimum_distance ] [ -Fxy_filter/z_filter ] [ -Ggap_distance ] [
12 -H[i][nrec] ] [ -M ] [ -Nnamestem ] [ -Qflags ] [ -S ] [ -V ] [ -Z ] [
13 -:[i|o] ] [ -b[i|o][s|S|d|D[ncol]|c[var1/...]] ] [ -f[i|o]colinfo ]
14
16 splitxyz reads a series of (x,y[,z]) records [or optionally
17 (x,y,z,d,h); see -S option] from standard input [or xyz[dh]file] and
18 splits this into separate lists of (x,y[,z]) series, such that each
19 series has a nearly constant azimuth through the x,y plane. There are
20 options to choose only those series which have a certain orientation,
21 to set a minimum length for series, and to high- or low-pass filter the
22 z values and/or the x,y values. splitxyz is a useful filter between
23 data extraction and pswiggle plotting, and can also be used to divide a
24 large x,y,z dataset into segments. The output is always in the ASCII
25 format; input may be ASCII or binary (see -b).
26 xyz[dh]file(s)
28 3 (but see -Z) [or 5] column ASCII file [or binary, see -b]
29 holding (x,y,z[,d,h]) data values. To use (x,y,z,d,h) input,
30 sorted so that d is non-decreasing, specify the -S option;
31 default expects (x,y,z) only. If no file is specified, splitxyz
32 will read from standard input.
33 -C Terminate a segment when a course change exceeding course_change
35 degrees of heading is detected.
36
38 -A Write out only those segments which are within +/- tolerance
39 degrees of azimuth in heading, measured clockwise from North, [0
40 - 360]. [Default writes all acceptable segments, regardless of
41 orientation].
42 -D Do not write a segment out unless it is at least minimum_dis‐
44 tance units long [0]
45 -F Filter the z values and/or the x,y values, assuming these are
47 functions of d coordinate. xy_filter and z_filter are filter
48 widths in distance units. If a filter width is zero, the fil‐
49 tering is not performed. The absolute value of the width is the
50 full width of a cosine-arch low-pass filter. If the width is
51 positive, the data are low-pass filtered; if negative, the data
52 are high-pass filtered by subtracting the low-pass value from
53 the observed value. If z_filter is non-zero, the entire series
54 of input z values is filtered before any segmentation is per‐
55 formed, so that the only edge effects in the filtering will hap‐
56 pen at the beginning and end of the complete data stream. If
57 xy_filter is non-zero, the data is first divided into segments
58 and then the x,y values of each segment are filtered separately.
59 This may introduce edge effects at the ends of each segment, but
60 prevents a low-pass x,y filter from rounding off the corners of
61 track segments. [Default = no filtering].
62 -G Do not let a segment have a gap exceeding gap_distance;
64 instead, split it into two segments. [Default ignores gaps].
65 -H Input file(s) has Header record(s). Number of header records
67 can be changed by editing your .gmtdefaults4 file. If used, GMT
68 default is 1 header record. Use -Hi if only input data should
69 have header records [Default will write out header records if
70 the input data have them]. Blank lines and lines starting with #
71 are always skipped. Not used with binary data.
72 -M Use Map units. Then x,y are in degrees of longitude, latitude,
74 distances are in kilometers, and angles are azimuths. [Default:
75 distances are cartesian in same units as x,y adn angles are
76 counter-clockwise from horizontal].
77 -N Create Named output files, writing each segment to a separate
79 file in the working directory named namestem.profile#, where #
80 increases consecutively from 1. [Default writes entire output
81 to stdout, separating segments by sub-headings that start with >
82 marks].
83 -Q Specify your desired output using any combination of xyzdh, in
85 any order. Do not space between the letters. Use lower case.
86 The output will be ASCII (or binary, see -bo) columns of values
87 corresponding to xyzdh [Default is -Qxyzdh (-Qxydh if -Z is
88 set)].
89 -S d and h is supplied. In this case, input contains x,y,z,d,h.
91 [Default expects (x,y,z) input, and d,h are computed from delta
92 x, delta y, according to -M option]
93 -V Selects verbose mode, which will send progress reports to stderr
95 [Default runs "silently"].
96 -Z Data have x,y only (no z-column).
98 -: Toggles between (longitude,latitude) and (latitude,longitude)
100 input and/or output. [Default is (longitude,latitude)]. Append
101 i to select input only or o to select output only. [Default
102 affects both].
103 -bi Selects binary input. Append s for single precision [Default is
105 d (double)]. Uppercase S or D will force byte-swapping.
106 Optionally, append ncol, the number of columns in your binary
107 input file if it exceeds the columns needed by the program. Or
108 append c if the input file is netCDF. Optionally, append
109 var1/var2/... to specify the variables to be read. [Default is
110 2, 3, or 5 input columns as set by -S, -Z].
111 -bo Selects binary output. Append s for single precision [Default
113 is d (double)]. Uppercase S or D will force byte-swapping.
114 Optionally, append ncol, the number of desired columns in your
115 binary output file. [Default is 1-5 output columns as set by
116 -Q].
117 -f Special formatting of input and/or output columns (time or geo‐
119 graphical data). Specify i or o to make this apply only to
120 input or output [Default applies to both]. Give one or more
121 columns (or column ranges) separated by commas. Append T (abso‐
122 lute calendar time), t (relative time in chosen TIME_UNIT since
123 TIME_EPOCH), x (longitude), y (latitude), or f (floating point)
124 to each column or column range item. Shorthand -f[i|o]g means
125 -f[i|o]0x,1y (geographic coordinates).
126
128 The ASCII output formats of numerical data are controlled by parameters
129 in your .gmtdefaults4 file. Longitude and latitude are formatted
130 according to OUTPUT_DEGREE_FORMAT, whereas other values are formatted
131 according to D_FORMAT. Be aware that the format in effect can lead to
132 loss of precision in the output, which can lead to various problems
133 downstream. If you find the output is not written with enough preci‐
134 sion, consider switching to binary output (-bo if available) or specify
135 more decimals using the D_FORMAT setting.
136
138 Suppose you want to make a wiggle plot of magnetic anomalies on seg‐
139 ments oriented approximately east-west from a cruise called cag71 in
140 the region -R300/315/12/20. You want to use a 100km low-pass filter to
141 smooth the tracks and a 500km high-pass filter to detrend the magnetic
142 anomalies. Try this:
143 gmtlist cag71 -R300/315/12/20 -Fxyzdh | splitxyz -A90/15 -F100/-500 -M
145 -D100 -S -V | pswiggle -R300/315/12/20 -Jm0.6 -Ba5f1:.cag71: -T1
146 -W0.75p -Ggray -Z200 > cag71_wiggles.ps
147 MGD-77 users: For this application we recommend that you extract d, h
149 from mgd77list rather than have splitxyz compute them separately.
150 Suppose you have been given a binary, double-precision file containing
152 lat, lon, gravity values from a survey, and you want to split it into
153 profiles named survey.profile# (when gap exceeds 100 km). Try this:
154 splitxyz survey.bin -Nsurvey -V -G100 -D100 -: -M -bi3
156
158 GMT(1), mgd77list(1), pswiggle(1)
159GMT 4.3.1 15 May 2008 SPLITXYZ(1)