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       blockmode - filter to block average (x,y,z) data by mode estimation.


       blockmode  [ xyz[w]file(s) ] -Ix_inc[m|c][/y_inc[m|c]] -Rwest/east/south/north[r] [ -C ] [
       -F ] [ -H[nrec] ] [ -L ] [ -Q ] [ -V ] [ -W[io] ] [ -: ] [ -bi[s][n] ] [ -bo[s][n] ]


       blockmode reads arbitrarily located (x,y,z) triples  [or  optionally  weighted  quadruples
       (x,y,z,w)]  from  standard  input  [or  xyz[w]file(s)]  and writes to standard output mode
       estimates of position and value for every non-empty block in a grid region defined by  the
       -R and -I arguments.  Either blockmean, blockmedian, or blockmode should be used as a pre-
       processor before running surface to avoid aliasing short wavelengths. These  routines  are
       also  generally  useful  for  decimating  or  averaging  (x,y,z)  data. You can modify the
       precision of the output format by editing the  D_FORMAT  parameter  in  your  .gmtdefaults
       file,  or  you  may  choose  binary  input  and/or output using single or double precision

              3 [or 4] column ASCII file(s) [or binary, see -b] holding (x,y,z[,w]) data  values.
              [w]  is  an  optional weight for the data.  If no file is specified, blockmode will
              read from standard input.

       -I     x_inc [and optionally y_inc] is the grid spacing. Append m to indicate minutes or c
              to indicate seconds.

       -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.


       -C     Use  the  center  of  the  block  as the output location [Default uses the modal xy
              location (but see -Q)].  -C overrides -Q.

       -F     Block centers have pixel registration. [Default: grid registration.] (Registrations
              are  defined  in  GMT  Cookbook Appendix B on grid file formats.) Each block is the
              locus of points nearest the grid value location. For  example,  with  -R10/15/10/15
              and  and  -I1:  with the -F option 10 <= (x,y) < 11 is one of 25 blocks; without it
              9.5 <= (x,y) < 10.5 is one of 36 blocks.

       -H     Input file(s) has Header record(s). Number of header  records  can  be  changed  by
              editing  your .gmtdefaults file. If used, GMT default is 1 header record.  Not used
              with binary data.

       -L     Indicates that the x column contains longitudes, which may differ from  the  region
              in -R by [multiples of] 360 degrees [Default assumes no periodicity].

       -Q     (Quicker) Finds mode z and mean (x, y) [Default finds mode x, mode y, mode z].

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

       -W     Weighted modifier[s]. Unweighted input and output has 3 columns x,y,z; Weighted i/o
              has  4  columns  x,y,z,w.  Weights can be used in input to construct weighted modal
              values in blocks. Weight sums can be reported in output for later combining several
              runs,  etc.  Use -W for weighted i/o, -Wi for weighted input only, -Wo for weighted
              output only. [Default uses unweighted i/o]

       -:     Toggles  between  (longitude,latitude)   and   (latitude,longitude)   input/output.
              [Default is (longitude,latitude)].  Applies to geographic coordinates only.

       -bi    Selects  binary input. Append s for single precision [Default is double].  Append n
              for the number of columns in the binary file(s).  [Default is 3 (or 4 if -W is set)

       -bo    Selects binary output. Append s for single precision [Default is double].


       To  find  5  by  5  minute  block  mode estimates from the double precision binary data in
       hawaii_b.xyg and output an ASCII table, try

       blockmode hawaii_b.xyg -R198/208/18/25 -I5m -bi3 > hawaii_5x5.xyg


       blockmean(1gmt),  blockmedian(1gmt),  gmt(1gmt),  gmtdefaults(1gmt),   nearneighbor(1gmt),
       surface(1gmt), triangulate(1gmt)

                                            1 Jan 2004                               BLOCKMODE(l)