Provided by: gmt_4.5.11-1build1_amd64 bug


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


       blockmode [ xyz[w]file(s) ] -Ixinc[unit][=|+][/yinc[unit][=|+]] -Rxmin/xmax/ymin/ymax[r] [
       -C ] [ -E ] [ -F  ]  [  -H[i][nrec]  ]  [  -Q  ]  [  -V  ]  [  -W[io]  ]  [  -:[i|o]  ]  [
       -b[i|o][s|S|d|D[ncol]|c[var1/...]] ] [ -f[i|o]colinfo ]


       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 .gmtdefaults4
       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. Optionally, append a suffix
              modifier.  Geographical (degrees) coordinates: Append m to indicate arc minutes  or
              c  to indicate arc seconds.  If one of the units e, k, i, or n is appended instead,
              the increment is assumed to be given  in  meter,  km,  miles,  or  nautical  miles,
              respectively,  and  will  be  converted  to the equivalent degrees longitude at the
              middle latitude of the region (the conversion depends on ELLIPSOID).  If /y_inc  is
              given  but set to 0 it will be reset equal to x_inc; otherwise it will be converted
              to degrees latitude.  All coordinates: If = is appended then the corresponding  max
              x  (east)  or y (north) may be slightly adjusted to fit exactly the given increment
              [by default the increment may be  adjusted  slightly  to  fit  the  given  domain].
              Finally, instead of giving an increment you may specify the number of nodes desired
              by appending + to the supplied integer argument; the increment is then recalculated
              from  the number of nodes and the domain.  The resulting increment value depends on
              whether you have selected  a  gridline-registered  or  pixel-registered  grid;  see
              Appendix  B  for details.  Note: if -Rgrdfile is used then grid spacing has already
              been initialized; use -I to override the values.

       -R     xmin, xmax, ymin, and ymax specify the Region of interest.  For geographic regions,
              these limits correspond to west, east, south, and north and you may specify them in
              decimal degrees or in [+-]dd:mm[][W|E|S|N] format.  Append r if  lower  left
              and  upper  right map coordinates are given instead of w/e/s/n.  The two shorthands
              -Rg and -Rd stand for global domain (0/360 and -180/+180 in longitude respectively,
              with  -90/+90  in  latitude).   Alternatively, specify the name of an existing grid
              file and the -R settings (and grid spacing, if  applicable)  are  copied  from  the
              grid.   For  calendar  time  coordinates  you  may  either  give  (a) relative time
              (relative to the selected TIME_EPOCH and in the selected  TIME_UNIT;  append  t  to
              -JX|x),  or  (b)  absolute time of the form [date]T[clock] (append T to -JX|x).  At
              least one of date and clock must be present; the T is always  required.   The  date
              string must be of the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or yyyy[-Www[-d]]
              (ISO week calendar), while the clock string must be  of  the  form  hh:mm:ss[.xxx].
              The  use  of  delimiters  and their type and positions must be exactly as indicated
              (however, input, output and plot formats are customizable; see gmtdefaults).


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

       -E     Provide  Extended report which includes s (the L1 scale of the mode), l, the lowest
              value, and h, the high value for each block. Output order becomes  x,y,z,s,l,h[,w].
              [Default outputs x,y,z[,w].  See -W for w output.

       -F     Force   pixel   node   registration  [Default  is  gridline  registration].   (Node
              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 -R
              10/15/10/15 and and -I 1:  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).  If used, the default number of header records
              is N_HEADER_RECS.  Use -Hi if only input data should have header  records  [Default
              will  write  out header records if the input data have them]. Blank lines and lines
              starting with # are always skipped.  Not used with binary data.

       -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 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  inputonly,  -Wo  for
              weighted output only.  [Default uses unweighted i/o].

       -:     Toggles  between (longitude,latitude) and (latitude,longitude) input and/or output.
              [Default is (longitude,latitude)].  Append i to select input only or  o  to  select
              output only.  [Default affects both].

       -bi    Selects  binary  input.   Append  s  for  single precision [Default is d (double)].
              Uppercase S or D will force byte-swapping.  Optionally, append ncol, the number  of
              columns  in your binary input file if it exceeds the columns needed by the program.
              Or append c if the input  file  is  netCDF.  Optionally,  append  var1/var2/...  to
              specify the variables to be read.  [Default is 3 (or 4 if -Wi is set)].

       -bo    Selects  binary  output.   Append  s  for single precision [Default is d (double)].
              Uppercase S or D will force byte-swapping.  Optionally, append ncol, the number  of
              desired  columns  in your binary output file.  [Default is 3 (or 4 if -Wo is set)].
              -E adds 3 additional columns.

       -f     Special formatting of input and/or output  columns  (time  or  geographical  data).
              Specify  i  or  o  to  make  this apply only to input or output [Default applies to
              both].  Give one or more columns (or column ranges) separated by commas.  Append  T
              (absolute calendar time), t (relative time in chosen TIME_UNIT since TIME_EPOCH), x
              (longitude), y (latitude), or f (floating point) to each  column  or  column  range
              item.  Shorthand -f[i|o]g means -f[i|o]0x,1y (geographic coordinates).


       The  ASCII  output  formats  of  numerical  data  are  controlled  by  parameters  in your
       .gmtdefaults4   file.    Longitude   and   latitude    are    formatted    according    to
       OUTPUT_DEGREE_FORMAT,  whereas other values are formatted according to D_FORMAT.  Be aware
       that the format in effect can lead to loss of precision in the output, which can  lead  to
       various problems downstream.  If you find the output is not written with enough precision,
       consider switching to binary output (-bo if available) or specify more decimals using  the
       D_FORMAT setting.


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

       blockmode hawaii_b.xyg -R 198/208/18/25 -I 5m -bi 3 > hawaii_5x5.xyg


       blockmean(1),  blockmedian(1),  GMT(1),   gmtdefaults(1),   nearneighbor(1),   surface(1),