Provided by: gmt_4.5.11-1build1_amd64 bug

NAME

       filter1d - Time domain filtering of 1-D time series

SYNOPSIS

       filter1d  [  infile  ]  -F<type><width>[mode]  [  -Dincrement  ]  [ -E ] [ -H[i][nrec] ] [
       -Iignore_val ] [ -Llack_width ] [ -Nn_cols/t_col ] [ -Qq_factor ] [ -Ssymmetry_factor ]  [
       -Tstart/stop/int ] [ -V ] [ -b[i|o][s|S|d|D[ncol]|c[var1/...]] ] [ -f[i|o]colinfo ]

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  the  filter  type.   Choose  among  convolution  and non-convolution filters.
              Append the filter code followed by the full filter width  in  same  units  as  time
              column. Available convolution filters are:
              (b) Boxcar: All weights are equal.
              (c) Cosine Arch: Weights follow a cosine arch curve.
              (g) Gaussian: Weights are given by the Gaussian function.
              (f)  Custom:  Instead  of width give name of a one-column file with your own weight
              coefficients.
              Non-convolution filters are:
              (m) Median: Returns median value.
              (p) Maximum likelihood probability (a mode estimator): Return modal value.  If more
              than  one mode is found we return their average value.  Append - or + to the filter
              width if you rather want to return the smallest or largest of the modal values.
              (l) Lower: Return the minimum of all values.
              (L) Lower: Return minimum of all positive values only.
              (u) Upper: Return maximum of all values.
              (U) Upper: Return maximum or all negative values only.
              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.
              In  the  case  of  L|U it is possible that no data passes the initial sign test; in
              that case the filter will return 0.0.

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).  If used, the default number of header records
              is N_HEADER_RECS.  Use -Hi if only input data should have header  records  [Default
              will  write  out header records if the input data have them]. Blank lines and lines
              starting with # are always skipped.

       -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
              "silently"].

       -bi    Selects binary input.  Append s for  single  precision  [Default  is  d  (double)].
              Uppercase  S or D will force byte-swapping.  Optionally, append ncol, the number of
              columns in your binary input file if it exceeds the columns needed by the  program.
              Or  append  c  if  the  input  file  is netCDF. Optionally, append var1/var2/... to
              specify the variables to be read.

       -bo    Selects binary output.  Append s for single  precision  [Default  is  d  (double)].
              Uppercase  S or D will force byte-swapping.  Optionally, append ncol, the number of
              desired columns in your binary output file.  [Default is same as input].

       -f     Special formatting of input and/or output  columns  (time  or  geographical  data).
              Specify  i  or  o  to  make  this apply only to input or output [Default applies to
              both].  Give one or more columns (or column ranges) separated by commas.  Append  T
              (absolute calendar time), t (relative time in chosen TIME_UNIT since TIME_EPOCH), x
              (longitude), y (latitude), or f (floating point) to each  column  or  column  range
              item.  Shorthand -f[i|o]g means -f[i|o]0x,1y (geographic coordinates).

ASCII FORMAT PRECISION

       The  ASCII  output  formats  of  numerical  data  are  controlled  by  parameters  in your
       .gmtdefaults4   file.    Longitude   and   latitude    are    formatted    according    to
       OUTPUT_DEGREE_FORMAT,  whereas other values are formatted according to D_FORMAT.  Be aware
       that the format in effect can lead to loss of precision in the output, which can  lead  to
       various problems downstream.  If you find the output is not written with enough precision,
       consider switching to binary output (-bo if available) or specify more decimals using  the
       D_FORMAT setting.

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  Gaussian  filter,  removing
       outliers, and output a filtered value every 2 km between 0 and 100 km:

       filter1d cruise.gmtd -T 0/1.0e5/2000 -FG 10000 -N 4/3 -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:

       filter1d v3312.dt -FM 50 -T 0/100000/25 -L 10 -S 0.3 > v3312_filt.dt

SEE ALSO

       GMT(1), sample1d(1)