grdfilter - Filter a .grdfile in the Time domain

grdfilterinput_file.grd-Dflag-F<type><width>-Goutput_file.grd[-Ix_inc[m|c][/y_inc[m|c]] ] [-N] [-Rwest/east/south/north[r] ] [-V]

grdfilterwill filter a .grdfile in the time domain, using a boxcar, cosine arch, gaussian, median, or mode filter, and computing distances by Cartesian or Spherical geometries. The output .grdfile 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.input_file.grdThe file of points to be filtered.-DDistanceflagtells how grid (x,y) relates to filterwidthas follows:flag= 0: grid (x,y) same units aswidth, Cartesian distances.flag= 1: grid (x,y) in degrees,widthin kilometers, Cartesian distances.flag= 2: grid (x,y) in degrees,widthin 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,widthin km, dx scaled by cosine(y), Cartesian distance calculation.flag= 4: grid (x,y) in degrees,widthin km, Spherical distance calculation.-FChoose one only ofbcgmpfor (b)oxcar, (c)osine Arch, (g)aussian, (m)edian, or maximum likelihood (p)robability (a mode estimator) filter and specify fullwidth.-Goutput_file.grdis the output of the filter.

-Ix_inc[and optionallyy_inc] is the output Increment. Appendmto indicate minutes, orcto indicate seconds. If the newx_inc,y_incare NOT integer multiples of the old ones (in the input data), filtering will be considerably slower. [Default: Same as input.]-NForce output grid to be pixel registered [Default gives gridline registration].-Rwest,east,south, andnorthdefines the Region of the output points. [Default: Same as input.]-VSelects 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

gmt, grdfft

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