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       filter1d - Time domain filtering of 1-D time series


       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] ]


       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(aussian), 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.


       -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 convolution.  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

       -bi    Selects binary input. Append s for single precision [Default is double].  Append  n
              for the number of columns in the binary file(s).

       -bo    Selects binary output. Append s for single precision [Default is double].


       To  filter  the  data  set  in  the  file  cruise.gmtd  containing  evenly spaced gravity,
       magnetics, topography, and distance  (in  m)  with  a  10  km  Gaussian  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 > filtered_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


       gmt(1gmt), sample1d(1gmt)

                                            1 Jan 2004                                FILTER1D(l)