1FILTER1D(1) GMT FILTER1D(1)
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6 filter1d - Do time domain filtering of 1-D data tables
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9 filter1d [ table ] -Ftype<width>[modifiers] [ -Dincrement ] [ -E ] [
10 -Llack_width ] [ -Nt_col ] [ -Qq_factor ] [ -Ssymmetry_factor ] [
11 -Tt_min/t_max/t_inc[+n] ] [ -V[level] ] [ -bbinary ] [ -dnodata ] [
12 -eregexp ] [ -fflags ] [ -ggaps ] [ -hheaders ] [ -iflags ] [ -oflags ]
13 [ -:[i|o] ]
14 Note: No space is allowed between the option flag and the associated
16 arguments.
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19 filter1d is a general time domain filter for multiple column time
20 series data. The user specifies which column is the time (i.e., the
21 independent variable). (See -N option below). The fastest operation
22 occurs when the input time series are equally spaced and have no gaps
23 or outliers and the special options are not needed. filter1d has
24 options -L, -Q, and -S for unevenly sampled data with gaps.
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27 -Ftypewidth[modifiers]
28 Sets the filter type. Choose among convolution and non-convolu‐
29 tion filters. Append the filter code followed by the full filter
30 width in same units as time column. By default we perform
31 low-pass filtering; append +h to select high-pass filtering.
32 Some filters allow for optional arguments and modifiers. Avail‐
33 able convolution filter types are:
34 (b) Boxcar: All weights are equal.
36 (c) Cosine Arch: Weights follow a cosine arch curve.
38 (g) Gaussian: Weights are given by the Gaussian function.
40 (f) Custom: Instead of width give name of a one-column file with
42 your own weight coefficients.
43 Non-convolution filter types are:
45 (m) Median: Returns median value.
47 (p) Maximum likelihood probability (a mode estimator): Return
49 modal value. If more than one mode is found we return their
50 average value. Append +l or +u if you rather want to return the
51 lowermost or uppermost of the modal values.
52 (l) Lower: Return the minimum of all values.
54 (L) Lower: Return minimum of all positive values only.
56 (u) Upper: Return maximum of all values.
58 (U) Upper: Return maximum or all negative values only.
60 Upper case type B, C, G, M, P, F will use robust filter ver‐
62 sions: i.e., replace outliers (2.5 L1 scale off median) with
63 median during filtering.
64 In the case of L|U it is possible that no data passes the ini‐
66 tial sign test; in that case the filter will return 0.0.
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69 table One or more ASCII (or binary, see -bi[ncols][type]) data table
70 file(s) holding a number of data columns. If no tables are given
71 then we read from standard input.
72 -Dincrement
74 increment is used when series is NOT equidistantly sampled. Then
75 increment will be the abscissae resolution, i.e., all abscissae
76 will be rounded off to a multiple of increment. Alternatively,
77 resample data with sample1d.
78 -E Include Ends of time series in output. Default loses half the
80 filter-width of data at each end.
81 -Llack_width
83 Checks for Lack of data condition. If input data has a gap
84 exceeding width then no output will be given at that point
85 [Default does not check Lack].
86 -Nt_col
88 Indicates which column contains the independent variable (time).
89 The left-most column is # 0, the right-most is # (n_cols - 1).
90 [Default is 0].
91 -Qq_factor
93 Assess Quality of output value by checking mean weight in convo‐
94 lution. Enter q_factor between 0 and 1. If mean weight < q_fac‐
95 tor, output is suppressed at this point [Default does not check
96 Quality].
97 -Ssymmetry_factor
99 Checks symmetry of data about window center. Enter a factor
100 between 0 and 1. If ( (abs(n_left - n_right)) / (n_left +
101 n_right) ) > factor, then no output will be given at this point
102 [Default does not check Symmetry].
103 -Tt_min/t_max/t_inc[+]
105 Make evenly spaced time-steps from t_min to t_max by t_inc
106 [Default uses input times]. Append +n to t_inc if you are speci‐
107 fying the number of equidistant points instead.
108 -V[level] (more ...)
110 Select verbosity level [c].
111 -bi[ncols][t] (more ...)
113 Select native binary input.
114 -bo[ncols][type] (more ...)
116 Select native binary output. [Default is same as input].
117 -d[i|o]nodata (more ...)
119 Replace input columns that equal nodata with NaN and do the
120 reverse on output.
121 -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
123 Only accept data records that match the given pattern.
124 -f[i|o]colinfo (more ...)
126 Specify data types of input and/or output columns.
127 -g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (more ...)
129 Determine data gaps and line breaks.
130 -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
132 Skip or produce header record(s).
133 -icols[+l][+sscale][+ooffset][,...] (more ...)
135 Select input columns and transformations (0 is first column).
136 -ocols[,...] (more ...)
138 Select output columns (0 is first column).
139 -:[i|o] (more ...)
141 Swap 1st and 2nd column on input and/or output.
142 -^ or just -
144 Print a short message about the syntax of the command, then
145 exits (NOTE: on Windows just use -).
146 -+ or just +
148 Print an extensive usage (help) message, including the explana‐
149 tion of any module-specific option (but not the GMT common
150 options), then exits.
151 -? or no arguments
153 Print a complete usage (help) message, including the explanation
154 of all options, then exits.
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157 The ASCII output formats of numerical data are controlled by parameters
158 in your gmt.conf file. Longitude and latitude are formatted according
159 to FORMAT_GEO_OUT, absolute time is under the control of FOR‐
160 MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point val‐
161 ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for‐
162 mat in effect can lead to loss of precision in ASCII output, which can
163 lead to various problems downstream. If you find the output is not
164 written with enough precision, consider switching to binary output (-bo
165 if available) or specify more decimals using the FORMAT_FLOAT_OUT set‐
166 ting.
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169 To filter the data set in the file cruise.gmtd containing evenly spaced
170 gravity, magnetics, topography, and distance (in m) with a 10 km Gauss‐
171 ian filter, removing outliers, and output a filtered value every 2 km
172 between 0 and 100 km:
173 gmt filter1d cruise.gmtd -T0/1.0e5/2000 -FG10000 -N3 -V > filtered_cruise.gmtd
175 Data along track often have uneven sampling and gaps which we do not
177 want to interpolate using sample1d. To find the median depth in a 50 km
178 window every 25 km along the track of cruise v3312, stored in v3312.dt,
179 checking for gaps of 10km and asymmetry of 0.3:
180 gmt filter1d v3312.dt -FM50 -T0/100000/25 -L10 -S0.3 > v3312_filt.dt
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184 gmt , sample1d , splitxyz
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187 2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
1885.4.5 Feb 24, 2019 FILTER1D(1)