NAME

       filter1d - Do time domain filtering of 1-D data tables

SYNOPSIS

       filter1d  [ table ]  -Ftype<width>[modifiers] [  -Dincrement ] [  -E ] [  -Llack_width ] [
       -Nt_col ] [  -Qq_factor ] [  -Ssymmetry_factor ] [  -Tt_min/t_max/t_inc[+n] ] [  -V[level]
       ]  [ -bbinary ] [ -dnodata ] [ -eregexp ] [ -fflags ] [ -ggaps ] [ -hheaders ] [ -iflags ]
       [ -oflags ] [ -:[i|o] ]

       Note: No space is allowed between the option flag and the associated arguments.

DESCRIPTION

       filter1d is a general time domain filter for multiple column time series  data.  The  user
       specifies  which  column  is  the  time  (i.e.,  the independent variable). (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.

REQUIRED ARGUMENTS

       -Ftypewidth[modifiers]
              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. By
              default we perform low-pass filtering; append +h  to  select  high-pass  filtering.
              Some  filters  allow  for  optional  arguments and modifiers. Available convolution
              filter types 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 filter types 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 +l or +u if you rather
              want to return the lowermost or uppermost 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.

OPTIONAL ARGUMENTS

       table  One  or  more  ASCII (or binary, see -bi[ncols][type]) data table file(s) holding a
              number of data columns. If no tables are given then we read from standard input.

       -Dincrement
              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.

       -Llack_width
              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].

       -Nt_col
              Indicates which column contains the  independent  variable  (time).  The  left-most
              column is # 0, the right-most is # (n_cols - 1).  [Default is 0].

       -Qq_factor
              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].

       -Ssymmetry_factor
              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].

       -Tt_min/t_max/t_inc[+]
              Make  evenly  spaced  time-steps  from  t_min to t_max by t_inc [Default uses input
              times]. Append +n to t_inc if you are specifying the number of  equidistant  points
              instead.

       -V[level] (more ...)
              Select verbosity level [c].

       -bi[ncols][t] (more ...)
              Select native binary input.

       -bo[ncols][type] (more ...)
              Select native binary output. [Default is same as input].

       -d[i|o]nodata (more ...)
              Replace input columns that equal nodata with NaN and do the reverse on output.

       -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
              Only accept data records that match the given pattern.

       -f[i|o]colinfo (more ...)
              Specify data types of input and/or output columns.

       -g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (more ...)
              Determine data gaps and line breaks.

       -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
              Skip or produce header record(s).

       -icols[+l][+sscale][+ooffset][,...] (more ...)
              Select input columns and transformations (0 is first column).

       -ocols[,...] (more ...)
              Select output columns (0 is first column).

       -:[i|o] (more ...)
              Swap 1st and 2nd column on input and/or output.

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows
              just use -).

       -+ or just +
              Print  an  extensive  usage  (help)  message,  including  the  explanation  of  any
              module-specific option (but not the GMT common options), then exits.

       -? or no arguments
              Print  a  complete  usage (help) message, including the explanation of all options,
              then exits.

ASCII FORMAT PRECISION

       The ASCII output formats of numerical data are controlled by parameters in  your  gmt.conf
       file.  Longitude  and latitude are formatted according to FORMAT_GEO_OUT, absolute time is
       under the control of FORMAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating  point
       values are formatted according to FORMAT_FLOAT_OUT. Be aware that the format in effect can
       lead to loss of precision in ASCII 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 FORMAT_FLOAT_OUT 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:

              gmt filter1d cruise.gmtd -T0/1.0e5/2000 -FG10000 -N3 -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:

              gmt filter1d v3312.dt -FM50 -T0/100000/25 -L10 -S0.3 > v3312_filt.dt

SEE ALSO

       gmt , sample1d , splitxyz

COPYRIGHT

       2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe