GRDCUT(l) GRDCUT(l)
NAME
grdcut - Extract a subregion out of a .grd file
SYNOPSIS
grdcut input_file.grd -Goutput_file.grd -Rwest/east/south/north[r] [ -V ]
DESCRIPTION
grdcut will produce a new output_file.grd file which is a subregion of input_file.grd. The subregion is specified with
-Rwest/east/south/north as in other programs; the specified range must not exceed the range of input_file.grd. If in doubt, run grdinfo to
check range. Complementary to grdcut there is grdpaste, which will join together two grdfiles along a common edge.
input_file.grd
this is the input .grd format file.
-Goutput_file.grd
this is the output .grd format file.
-R west, east, south, and north specify the Region of interest. To specify boundaries in degrees and minutes [and seconds], use the
dd:mm[:ss] format. Append r if lower left and upper right map coordinates are given instead of wesn. This defines the subregion to
be cut out.
OPTIONS -V Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].
EXAMPLES
Suppose you have used surface to grid ship gravity in the region between 148E - 162E and 8N - 32N, and you do not trust the gridding near
the edges, so you want to keep only the area between 150E - 160E and 10N - 30N, then:
grdcut grav_148_162_8_32.grd -Ggrav_150_160_10_30.grd -R150/160/10/30 -V
SEE ALSO grdpaste(1gmt), grdinfo(1gmt), gmt(1gmt)
1 Jan 2004 GRDCUT(l)
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GRDFILTER(l) GRDFILTER(l)
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)