grdfilter - Filter a .grd file in the Time domain
grdfilter input_file.grd -Dflag -F<type><width> -Goutput_file.grd [
-Ix_inc[m|c][/y_inc[m|c]] ] [ -N ] [ -Rwest/east/south/north[r] ] [ -V
grdfilter will filter a .grd file in the time domain, using a boxcar,
cosine arch, gaussian, median, or mode filter, and computing distances
by Cartesian or Spherical geometries. The output .grd file can
optionally be generated in a sub-Region of the input, and / or at 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; also, if the filter is low-pass,
then the output may be needed less frequently sampled than the input.
The file of points to be filtered.
-D Distance flag tells how grid (x,y) relates to filter width as
flag = 0: grid (x,y) same units as width, Cartesian distances.
flag = 1: grid (x,y) in degrees, width in kilometers, Cartesian
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
-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.
-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
-N Force output grid to be pixel registered [Default gives gridline
-R west, east, south, and north defines the Region of the output
points. [Default: Same as input.]
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
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
Man(1) output converted with