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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