blockmode

       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] [ -C ] [ -F ] [ -H[nrec] ] [ -L
       ] [ -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 alias­
       ing 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 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

       -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.
              header records can be changed by editing your .gmt­
              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].

       -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  (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) columns].

       -bo    Selects binary output. Append s for  single  preci­
              sion [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(l),  blockmedian(l),   gmt(l),   gmtdefaults(l),
       nearneighbor(l), surface(l), triangulate(l)