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 operation
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. Alter-
natively, 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_fac-
tor, 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)
GMT3.4.6 1 Jan 2005 FILTER1D(l)
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