## NAME

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

## SYNOPSIS

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

## DESCRIPTION

          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 storage.

          xyz[w]file(s)
               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.

## OPTIONS

          -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.

          -N   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 -N option 10 <= (x,y) < 11
               is one of 25 blocks; without it 9.5 <= (x,y) < 10.5 is one of 36
               blocks.

          -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 "silently"].

          -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)].

          -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) columns].

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

## EXAMPLES

          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

## SEE ALSO

          blockmean, blockmedian, gmt, gmtdefaults, nearneighbor, surface,
          triangulate