grdfilter

       grdfilter - Filter a .grd file in the Time domain

SYNOPSIS

       grdfilter  input_file.grd  -Dflag  -F<type><width>  -Gout­
       put_file.grd    [    -Ix_inc[m|c][/y_inc[m|c]]     ]     [
       -Rwest/east/south/north[r] ] [ -T ] [ -V ]

DESCRIPTION

       grdfilter will filter a .grd file in the time domain using
       a boxcar, cosine arch, gaussian, median,  or  mode  filter
       and  computing  distances  using  Cartesian  or  Spherical
       geometries.  The output .grd file can optionally be gener­
       ated  as  a  sub-Region  of  the  input  and/or with a new
       -Increment. In this way, one may have "extra space" in the
       input data so that the edges will not be used and the out­
       put can be within one-half- width of the input  edges.  If
       the  filter  is low-pass, then the output may be less fre­
       quently sampled than the input.

       input_file.grd
              The file of points to be filtered.

       -D     Distance flag tells how grid (x,y) relates to  fil­
              ter width as follows:

              flag = 0: grid (x,y) same units as width, Cartesian
              distances.
              flag = 1: grid (x,y) in degrees, width  in  kilome­
              ters, Cartesian distances.
              flag  =  2:  grid (x,y) in degrees, width in km, dx
              scaled by cos(middle y), Cartesian distances.

              The above options are fastest  because  they  allow
              weight  matrix  to be computed only once.  The next
              two  options  are  slower  because  they  recompute
              weights for each East-West scan line.

              flag  =  3:  grid (x,y) in degrees, width in km, dx
              scaled by cosine(y),  Cartesian  distance  calcula­
              tion.
              flag  =  4:  grid  (x,y)  in  degrees, width in km,
              Spherical distance calculation.

       -F     Choose one only of  bcgmp  for  (b)oxcar,  (c)osine
              Arch,  (g)aussian,  (m)edian, or maximum likelihood
              (p)robability (a mode estimator) filter and specify
              full width.

       -G     output_file.grd is the output of the filter.

OPTIONS

       -I     x_inc  [and  optionally y_inc] is the output Incre­
              integer multiples of the old  ones  (in  the  input
              data),   filtering  will  be  considerably  slower.
              [Default: Same as input.]

       -R     west, east, south, and north defines the Region  of
              the output points. [Default: Same as input.]

       -T     Toggle the node registration for the output grid so
              as  to  become  the  opposite  of  the  input  grid
              [Default  gives  the same registration as the input
              grid].

       -V     Selects verbose  mode,  which  will  send  progress
              reports to stderr [Default runs "silently"].

EXAMPLES

       Suppose that north_pacific_dbdb5.grd is a file of 5 minute
       bathymetry from 140E to 260E and 0N to 50N, and  you  want
       to find the medians of values within a 300km radius (600km
       full width) of the output points, which you choose  to  be
       from  150E to 250E and 10N to 40N, and you want the output
       values every 0.5 degree. Using spherical distance calcula­
       tions, you need:

       grdfilter  north_pacific_dbdb5.grd  -Gfiltered_pacific.grd
       -Fm600 -D4 -R150/250/10/40 -I0.5 -V

SEE ALSO

       gmt(l), grdfft(l)