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filter1d(1)                           GMT                          filter1d(1)


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


       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


       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.


              Sets  the filter type. Choose among convolution and non-convolu-
              tion 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. Avail-
              able 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  ver-
              sions:  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  ini-
              tial sign test; in that case the filter will return 0.0.


       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.

              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.

              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].

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

              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

              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].

              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 speci-
              fying the number of equidistant points instead.

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

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

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

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

       -e[~]^<i>apattern^<i>a | -e[~]/regexp/[i] (more a|)
              Only accept data records that match the given pattern.

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

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

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

       -icols[+l][+sscale][+ooffset][,^<i>a|] (more a|)
              Select input columns and transformations (0 is first column).

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

       -:[i|o] (more a|)
              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 explana-
              tion 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.


       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   FOR-
       MAT_DATE_OUT  and FORMAT_CLOCK_OUT, whereas general floating point val-
       ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for-
       mat  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  set-


       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:

              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


       gmt(1), sample1d(1), splitxyz(1)


       2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe

5.4.2                            Jun 24, 2017                      filter1d(1)

gmt5 5.4.2 - Generated Wed Jun 28 15:18:32 CDT 2017
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