Provided by: gmt_4.5.11-1build1_amd64 bug

NAME

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

SYNOPSIS

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

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 .gmtdefaults4 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.  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[:ss.xxx][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).

OPTIONS

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

       -E     Provide Extended report which includes s (the standard deviation of the  mean),  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.

       -S     Use  -Sz to report the sum of all z-values inside a block, or -Sw to report the sum
              of weights [Default reports mean value]. If -Sw is  selected  and  no  weights  are
              supplied  (i.e.,  no -W given), then the weight sum will equal the number of points
              inside each block.

       -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  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).

ASCII FORMAT PRECISION

       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.

EXAMPLES

       To find 5 by 5 minute block mean values from the ASCII data in hawaii.xyg, run

       blockmean hawaii.xyg -R 198/208/18/25 -I 5m > hawaii_5x5.xyg

SEE ALSO

       blockmedian(1),   blockmode(1),   gmtdefaults(1),   GMT(1),  nearneighbor(1),  surface(1),
       triangulate(1)