## NAME

          blockmean - filter to block average (x,y,z) data by L2 norm

## SYNOPSIS

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

## DESCRIPTION

          blockmean 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 a mean 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, blockmean 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.

          -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 mean 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)].

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

## EXAMPLES

          To find 5 by 5 minute block means from the ASCII data in hawaii.xyg,
          try

          blockmean hawaii.xyg -R198/208/18/25 -I5m > hawaii_5x5.xyg

## SEE ALSO

          blockmedian, blockmode, gmtdefaults, gmt, nearneighbor, surface,
          triangulate