blockmean

       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] [ -C ] [ -F ] [ -H[nrec] ] [ -L
       ] [ -S ] [ -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  use­
       ful for decimating or averaging (x,y,z) data. You can mod­
       ify 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 sec­
              onds.

       -R     west, east, south, and north specify the Region  of
              interest. To specify boundaries in degrees and min­
              utes [and  seconds],  use  the  dd:mm[:ss]  format.
              Append  r if lower left and upper right map coordi­
              nates are given instead of wesn.

OPTIONS

       TP -C Use the center of the block as the  output  location
       [Default uses the mean location].

       -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.

              defaults 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  [multi­
              ples  of] 360 degrees [Default assumes no periodic­
              ity].

       -S     Report the sum  of  all  z-values  inside  a  block
              [Default reports mean value].

       -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  (lati­
              tude,longitude) input/output. [Default  is  (longi­
              tude,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 preci­
              sion [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(l),  blockmode(l),   gmtdefaults(l),   gmt(l),
       nearneighbor(l), surface(l), triangulate(l)