NAME

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

SYNOPSIS

       filter1d  [  table  ]  type<width>[mode]  [  increment  ]  [  ] [ ignore_val ] [ lack_width ] [ t_col ] [
       q_factor ] [ symmetry_factor ] [ t_min/t_max/t_inc[+] ] [ [level] ] [  -b<binary>  ]  [  -d<nodata>  ]  [
       -f<flags> ] [ -g<gaps> ] [ -h<headers> ] [ -i<flags> ] [ -o<flags> ] [ -:[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

       -Ftype<width>[mode]
              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.

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.

       -Iignore_val
              To ignore values; If an input value equals ignore_val it will be set to NaN.

       -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 + 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.

       -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 (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 use just -).

       -+ 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 options, then exits.

       --version
              Print GMT version and exit.

       --show-datadir
              Print full path to GMT share directory and exit.

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, whereas other values are formatted  according  to
       FORMAT_FLOAT_OUT.  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
       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

       2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe

5.2.1                                           January 28, 2016                                  FILTER1D(1gmt)