NAME

       grdfilter - Filter a .grd file in the Time domain

SYNOPSIS

       grdfilter  input_file.grd  -Dflag  -F<type><width>  -Goutput_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 generated 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 output can be within one-
       half- width of the input edges. If the filter is low-pass, then the output may be less frequently sampled
       than the input.

       input_file.grd
              The file of points to be filtered.

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

              flag = 0: grid (x,y) same units as width, Cartesian distances.
              flag = 1: grid (x,y) in degrees, width in kilometers, 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
              calculation.
              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  Increment. Append m to indicate minutes, or c to
              indicate seconds.  If the new x_inc, y_inc are NOT 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 calculations, you need:

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

SEE ALSO

       gmt(1gmt), grdfft(1gmt)

                                                   1 Jan 2004                                       GRDFILTER(l)