manpagez: man pages & more
man blockmean(1)
Home | html | info | man
blockmean(1)                          GMT                         blockmean(1)


       blockmean - Block average (x, y, z) data tables by L2 norm


       blockmean [ table ]
        -Rregion  [   -C  ]  [   -E[p]  ]  [   -S[m|n|s|w]  ] [  -V[level] ] [
       -W[i|o][+s] ] [ -bbinary ] [ -dnodata ] [ -eregexp  ]  [  -fflags  ]  [
       -hheaders ] [ -iflags ] [ -oflags ] [ -r ] [ -:[i|o] ]

       Note:  No  space  is allowed between the option flag and the associated


       blockmean reads arbitrarily  located  (x,y,z)  triples  [or  optionally
       weighted  quadruples  (x,y,z,w)]  from  standard  input  [or table] 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 rou-
       tines are also generally useful for  decimating  or  averaging  (x,y,z)
       data.  You can modify the precision of the output format by editing the
       FORMAT_FLOAT_OUT parameter in your gmt.conf file,  or  you  may  choose
       binary input and/or output to avoid loss of precision.


              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 s to indicate arc seconds.
              If one of the units e, f, k, M, n or u is appended instead,  the
              increment  is assumed to be given in meter, foot, km, Mile, nau-
              tical mile or US survey foot, respectively,  and  will  be  con-
              verted  to  the equivalent degrees longitude at the middle lati-
              tude of the region (the conversion depends  on  PROJ_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  coordi-
              nates:  If +e 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 +n to
              the supplied integer argument; the increment  is  then  recalcu-
              lated  from  the  number  of nodes and the domain. The resulting
              increment value depends on whether you  have  selected  a  grid-
              line-registered  or  pixel-registered grid; see App-file-formats
              for details. Note: if -Rgrdfile is used then  the  grid  spacing
              has already been initialized; use -I to override the values.

       -Rxmin/xmax/ymin/ymax[+r][+uunit] (more a|)
              Specify the region of interest.


       table  3 [or 4, see -W] column ASCII data table file(s) [or binary, see
              -bi] 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.

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

       -E[p]  Provide Extended report which includes s (the standard deviation
              about 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 out-
              puts x,y,z[,w]. See -W for w output.  If -Ep is used  we  assume
              weights are 1/(sigma squared) and s becomes the propagated error
              of the mean.

              Use -Sn to report the number of points inside each block, -Ss to
              report the sum of all z-values inside a block, -Sw to report the
              sum of weights [Default (or -Sm reports mean value].

       -V[level] (more a|)
              Select verbosity level [c].

              Weighted modifier[s]. Unweighted input and output have 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  for  each  block.
              Weight  sums  can be reported in output for later combining sev-
              eral runs, etc. Use -W for weighted i/o, -Wi for weighted  input
              only, and -Wo for weighted output only. [Default uses unweighted
              i/o]. If your weights are  actually  uncertainties  (one  sigma)
              then append +s and we compute weight = 1/sigma.

       -bi[ncols][t] (more a|)
              Select native binary input. [Default is 3 (or 4 if -Wi is set)].

       -bo[ncols][type] (more a|)
              Select native binary output. [Default is  3  (or  4  if  -Wo  is
              set)].  -E  adds 3 additional columns.  The -Sn option will work
              with only 2 input columns (x and y).

       -d[i|o]nodata (more a|)
              Replace input columns that equal nodata  with  NaN  and  do  the
              reverse on output.

       -e[~]^<i>apattern^<i>a | -e[~]/regexp/[i] (more a|)
              Only accept data records that match the given pattern.

       -f[i|o]colinfo (more a|)
              Specify data types of input and/or output columns.

       -h[i|o][n][+c][+d][+rremark][+rtitle] (more a|)
              Skip or produce header record(s).

       -icols[+l][+sscale][+ooffset][,^<i>a|] (more a|)
              Select input columns and transformations (0 is first column).

       -ocols[,a|] (more a|)
              Select output columns (0 is first column).

       -r (more a|)
              Set  pixel node registration [gridline]. Each block is the locus
              of points nearest the grid value location. Consider  an  example
              with -R10/15/10/15 and -I1: With the -r option, 10 <= (x,y) < 11
              is one of 25 blocks; without it 9.5 <= (x,y) < 10.5 is one of 36

       -:[i|o] (more a|)
              Swap 1st and 2nd column on input and/or output.

       -^ or just -
              Print  a  short  message  about  the syntax of the command, then
              exits (NOTE: on Windows just use -).

       -+ or just +
              Print an extensive usage (help) message, including the  explana-
              tion  of  any  module-specific  option  (but  not the GMT common
              options), then exits.

       -? or no arguments
              Print a complete usage (help) message, including the explanation
              of all options, then exits.


       The ASCII output formats of numerical data are controlled by parameters
       in your gmt.conf file. Longitude and latitude are  formatted  according
       to   FORMAT_GEO_OUT,  absolute  time  is  under  the  control  of  FOR-
       MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point  val-
       ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for-
       mat in effect can lead to loss of precision in ASCII 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 FORMAT_FLOAT_OUT set-


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

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


       blockmedian(1), blockmode(1), gmt(1), gmt.conf(5), greenspline(1),
       nearneighbor(1), sphtriangulate(1), surface(1), triangulate(1)


       2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe

5.4.2                            Jun 24, 2017                     blockmean(1)

gmt5 5.4.2 - Generated Wed Jun 28 14:51:09 CDT 2017
© 2000-2021
Individual documents may contain additional copyright information.