NAME
filter1d - Time domain filtering of 1-D time series
SYNOPSIS
filter1d [ infile ] -F<type><width> [ -Dincrement ] [ -E ] [ -H[nrec] ]
[ -Iignore_val ] [ -Llack_width ] [ -Nn_cols/t_col ] [ -Qq_factor ] [
-Ssymmetry_factor ] [ -Tstart/stop/int ] [ -V ] [ -bi[s][n] ] [
-bo[s][n] ]
DESCRIPTION
filter1d is a general time domain filter for multiple column time
series data. The user specifies the number of columns of input and
which column is the time. (See -N option below). The fastest opera-
tion occurs when the input time series are equally spaced and have no
gaps or outliers and the special options are not needed. filter1d has
options L, Q, and S for unevenly sampled data with gaps.
infile Multi-column ASCII (or binary, see -b) file holding data values
to be filtered.
-F sets Filtertype, type is one of b(oxcar), c(osine arch), g(aus-
sian), m(edian), or p(maximum likelihood Probability estimator
-- a mode estimator), and specify full filter width in same
units as time column, OR, use -Ffname to give the name of a one-
column file of your own coefficients. Upper case type B, C, G,
M, P, F will use robust filter versions: i.e., replace outliers
(2.5 L1 scale off median) with median during filtering.
OPTIONS
-D increment is used when series is NOT equidistantly sampled.
Then increment will be the abscissae resolution, i.e., all
abscissae will be rounded off to a multiple of increment.
Alternatively, resample data with sample1d.
-E Include Ends of time series in output. Default loses half the
filter-width of data at each end.
-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.
-I To ignore values; If an input value equals ignore_val it will be
set to NaN.
-L Checks for Lack of data condition. If input data has a gap
exceeding width then no output will be given at that point
[Default does not check Lack].
-N Sets number of columns in input and which column contains the
independent variable (time). The left-most column is # 0, the
right-most is # (n_cols - 1). [Default is n_cols = 2, t_col =
0; i.e., file has t, f(t) pairs].
-Q assess Quality of output value by checking mean weight in convo-
lution. Enter q_factor between 0 and 1. If mean weight <
q_factor, output is suppressed at this point [Default does not
check Quality].
-S Checks symmetry of data about window center. Enter a factor
between 0 and 1. If ( (abs(n_left - n_right)) / (n_left +
n_right) ) > factor, then no output will be given at this point
[Default does not check Symmetry].
-T Make evenly spaced timesteps from start to stop by int [Default
uses input times].
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
-bi Selects binary input. Append s for single precision [Default is
double]. Append n for the number of columns in the binary
file(s).
-O Selects Overlay plot mode [Default initializes a new plot sys-
tem].
EXAMPLES
To filter the data set in the file cruise.gmtd containing evenly spaced
gravity, magnetics, topography, and distance (in m) with a 10 km Gaus-
sian filter, removing outliers, and output a filtered value every 2 km
between 0 and 100 km, try
filter1d cruise.gmtd -T0/1.0e5/2000 -FG10000 -N4/3 -V > fil-
tered_cruise.gmtd
Data along track often have uneven sampling and gaps which we do not
want to interpolate using sample1d. To find the median depth in a 50
km window every 25 km along the track of cruise v3312, stored in
v3312.dt, checking for gaps of 10km and asymmetry of 0.3, try
filter1d v3312.dt -FM50 -T0/100000/25 -L10 -S0.3 > v3312_filt.dt
SEE ALSO
gmt(l), sample1d(l)
VERSION DATE FILTER1D(l)
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